AGE vs EPOCH

CRATER IMPACT AGE vs EXTINCTION EPOCH

by: Charles O’Dale

In my articles I use the term crater to define a circular impact depression and the term structure to define an impact crater that is severely altered by erosion.

Also see:  CRATER ABSOLUTE AGE

    1. INTRODUCTION
    2. PLANETARY ACCRETION: 4.56 BILLION
    3. HADEAN: 4.56 BILLION -3.8 BILLION
    4. ARCHEAN: 4.0 BILLION -2.5 BILLION
    5. PROTEROZOIC: 2.5 BILLION – 542 MILLION
    6. CAMBRIAN: 542 – 488 MILLION
    7. ORDOVICIAN: 488 – 443 MILLION
    8. ~450 Ma – ORDOVICIAN EXTINCTION
    9. SILURIAN: 443 – 416 MILLION
    10. DEVONIAN: 416 – 359.2 MILLION
    11. ~374 Ma – LATE DEVONIAN EXTINCTION
    12. MISSISSIPPIAN: 359.2 – 318 MILLION
    13. PENNSYLVANIAN: 318 – 299 MILLION
    14. PERMIAN: 299 – 252.2 MILLION
    15. 252.28 Ma – PERMIAN-TRIASSIC EXTINCTION
    16. TRIASSIC: 252.2 – 199.6 MILLION
    17. ~214 Ma – LATE TRIASSIC (extinction at the Carnian/Norian boundary – 227 Ma)
    18. 201.3 Ma – TRIASSIC-JURASSIC EXTINCTION
    19. DINOSAUR  EVOLUTION AT THE TRIASSIC (Tr-J) vs END-CRETACEOUS (K-Pg) EXTINCTIONS
    20. JURASSIC: 199.6 – 145.5 MILLION
    21. CRETACEOUS: 145.5 – 65.5 MILLION
    22. 66.043 ±0.011 mA – CRETACEOUS-PALEOGENE EXTINCTION
    23. PALEOCENE: 65.5 – 55.8 MILLION
    24. EOCENE: 55.8 – 33.9 MILLION
    25. 33.9 Ma – EOCENE-OLIGOCENE EXTINCTION
    26. OLIGOCENE: 33.9 – 23 MILLION
    27. MIOCENE: 23 – 5.3 MILLION
    28. PLIOCENE: 5.3 – 1.8 MILLION
    29. PLEISTOCENE: 1.8 MILLION – 10 THOUSAND
    30. ~12,000 years – YOUNGER DRYAS (YD) EXTINCTION
    31. HOLOCENE: 10 THOUSAND – PRESENT
    32. 50 MILLION YEARS IN THE FUTURE
    33. GEOLOGIC PERIODS vs IMPACT
    34.  REFERENCE

 


1. INTRODUCTION

An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the amount of life on earth. Such an event is identified by a sharp change in the diversity and abundance of macroscopic life. It occurs when the rate of extinction increases with respect to the rate of speciation. Because the majority of diversity and biomass on Earth is microbial, and thus difficult to measure, recorded extinction events affect the easily observed, biologically complex component of the biosphere rather than the total diversity.

Over 98% of documented species are now extinct, but extinction occurs at an uneven rate. Based on the fossil record, the background rate of extinctions on Earth is about two to five taxonomic families of marine invertebrates and vertebrates every million years. Marine fossils are mostly used to measure extinction rates because of their superior fossil record and stratigraphic range compared to land organisms.

Since life began on Earth, several major mass extinctions have significantly exceeded the background extinction rate. In the past 540 million years there have been five major events when over 50% of animal species died. Mass extinctions seem to be a Phanerozoic phenomenon, with extinction rates low before large complex organisms arose. Estimates of the number of major mass extinctions in the last 540 million years range from as few as five to more than twenty. These differences stem from the threshold chosen for describing an extinction event as “major”, and the data chosen to measure past diversity.

The Cretaceous–Paleogene extinction event, which occurred approximately 66 million years ago (Ma), was a large-scale mass extinction of animal and plant species in a geologically short period of time. It is generally believed that the K-Pg extinction was triggered by a massive comet/asteroid impact and its catastrophic effects on the global environment, including a lingering impact winter that made it impossible for plants and plankton to carry out photosynthesis. Various other impacts might also be associated with extinction events.

Evidence that an impact event may have caused the Cretaceous–Paleogene extinction event has led to speculation that similar impacts may have been the cause of other extinction events, including the P–Tr extinction, and therefore to a search for evidence of impacts at the times of other extinctions and for large impact craters of the appropriate age. Below I have listed impact structures whose ages coincide with recorded extinctions. Evidence for a related impact, if any, is documented.


2. PLANETARY ACCRETION 4.56 BILLION


3. HADEAN: 4.56 BILLION -4.0 BILLION

 

  • Formation of the Earth;
  • A huge planetoid crushes into Earth & splits off Moon;
  • Massive meteor bombardments pound Earth and Moon;
  • Interior of the molten Earth separates into layers;
  • Dense, very hot atmosphere of hydrogen, CO², steam, ammonia & methane – no oxygen;
  • Boiling steam begins to condense into oceans;
  • Earliest known rocks on Earth date from the Hadean;
  • Organic chemical components of the building blocks;
    of life (amino acids, RNA and DNA) first appear.

4. ARCHEAN: 4.0 BILLION -2.5 BILLION

  • The Earth’s temperature 3 times hotter than today;
  • The Earth’s crust very thin;
  • Enormous volcanic and tectonic activity;
  • Protocontinents begin to form over hotspots;
  • Dense, hot atmosphere of CO², methane and ammonia;
  • Oceans hot, acidic and filled with dissolved metals;
  • First life appears as simple prokaryote bacteria;
  • Single-celled archaea extemophiles appear;
  • Cyanobacteria appear & begin forming stromatolites;
  • Cyanobacteria develop photosynthesis & begin pumping oxygen into the atmosphere.
Rodinia formed at c. 1.23 Ga by accretion and collision of fragments produced by breakup of an older supercontinent, and assembled by global-scale 2.1–1.82 Ga collisional events. Orogenic belts of 1.1 Ga age are highlighted in green.

Orogeny is an event that leads to a large structural deformation of the Earth’s lithosphere (crust and uppermost mantle) due to the interaction between tectonic plates.

  •  Earth was still about three times as hot as it is today;
  • Most of the Earth was covered with oceans;
  • Earth’s atmosphere was mainly carbon dioxide;
  • low oxygen levels;
  • Few small cratons formed by volcanoes;
  • Most of the rocks were igneous or metamorphic like granite or quartz;
  • Earliest sedimentary rocks like sandstone also formed in the oceans;
  • Earliest living cells formed in the oceans, evolved into simple prokaryote cells;
  • By three billion years ago, prokaryote cells evolved photosynthesis;
  • excreted (pooped out) oxygen;
  • Iron and sulfur rocks mixed with early oxygen atoms to make rusty red rocks and limestone;
  • Many large asteroids that hit the Earth during the Archaean Eon. 
Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Hudson Bay Arc >450  <4,600  Arc rock age IMPROBABLE Multi ring basin? No impact metamorphism found

5. PROTEROZOIC: 2.5 BILLION – 542 MILLION

600 million years ago, a supercontinent known as Rodina split apart, and a vast ocean filled the basin. Map courtesy of CR Scotese, PALEOMAP Project
  • multicellular organisms appear;
  • 2.45–1.85 Ga: O2 produced, but absorbed in oceans and seabed rock;
  • 1.85–0.85 Ga: O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer;
  • Rodinia Supercontinent comes together[
  • All oceans merged into one – Mirovia;
  • Considerable mountain building;
  • Ocean and atmosphere reach chemical composition approximately same as today;
  • All land is barren, lifeless desert.
Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Sudbury, Ontario 250 1852 +4/-3 U-Pb zircon CONFIRMED Multi-ring? Sudbury Distal Ejecta
Skeleton Lake, Ontario 3.5 ~800 Geological dating PROBABLE Simple
Beaverhead, Montana/Idaho ~100 ~600 K-Ar, 40Ar/39Ar and Rb-Sr CONFIRMED Peak ring Allochthonous
Holleford, Ontario 2.35 550 ±100 Geological dating CONFIRMED Simple Overflight of Holleford Crater

6. CAMBRIAN: 542 – 488 MILLION

500 million years ago a chunk of the supercontinent Pannotia drifted north and split into three masses, forming Laurentia (present-day North America), Baltica (present-day northern Europe), and Siberia. In shallow waters, the first multicellular animals with exoskeletons appeared, and an explosion of life began. Map courtesy of CR Scotese, PALEOMAP Project
  • multicellular organisms gradually became more common, produced the first representatives of all modern animal phyla;
  • mean surface temperature 7 °C above modern level;
  • sea level 30m above present day, rising steadily to 90m;
  • Pannotia splits up into masses that will become Laurentia and Gondwana;
  • Panthalassic Ocean forms with wide shallow seas;
  • Climate very warm with high oxygen content;
  • All land is barren, lifeless desert;
  • First vertebrates appear;
  • Many strange “experimental” forms appear, but many
    die out in mass extinction at the end of the period.

 

Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Touchwood Hills, Saskatchewan >200 >541 Post Williston Basin deposit IMPROBABLE Multi-ring Basin?
Can-Am, Lake Huron 100 ~500 Geological dating PROBABLE Complex Underwater in Lake Huron
Glover Bluff, Wisconsin 8 <500 Geological dating CONFIRMED Complex
Presqu’ile, Quebec 24 <500 Geological dating CONFIRMED Complex High level erosion
Newporte, North Dakota 3.2 <500 Geological biostratigraphic dating CONFIRMED Simple No surface evidence

7. ORDOVICIAN: 488 – 443 MILLION

  • 86% of species lost
  • diversity of life increases, fish are the first true vertebrates;
  • O2 68 % of modern level;
  • mean surface temperature 2 °C above modern level;
  • sea level 180m above present day, rising to 220 m and falling sharply to 140 m in end-Ordovician glaciation;
  • 100 times as many meteorites struck the Earth per year during the Ordovician compared with today;
  • Appalachians first formed, Laurentia and Gondwana hover near equator, wide shallow seas; climate warm but later cools;
  • First life on land – primitive liverwort plants and fungi;
  • The period ends in ice age and extinction.

 

Name Diameter (km) Age (megayears) Dating method Morphological type Notes
James River, Alberta 4.8 <480 Geological dating PROBABLE Complex No surface expression
Clearwater East, Quebec 26 ~460–470 Rb-Sr melt rocks CONFIRMED Complex Chondrite-type
Calvin, Michigan 7.24 450 ± 10 Geological dating CONFIRMED Complex
Pilot Lake, North West Territories 6 445 ± 2 K-Ar, 40Ar/39Ar and Rb-Sr CONFIRMED Complex Dating based on one sample
Bear Swamp, New York 3.5 ~444 Geological dating PROBABLE Simple No surface expression
Glasford, Illinois ~4 443.8-485.4 Geological dating CONFIRMED Complex Shattercones, shock metamorphism

8. ~450 Ma – ORDOVICIAN EXTINCTION

86% of species lost — Graptolite 2-3 cm length

Graptolites, like most Ordovician life, were sea creatures. They were filter-feeding animals and colony builders. Their demise over about a million years was probably caused by a short, severe ice age that lowered sea levels, possibly triggered by the uplift of the Appalachians. The newly exposed silicate rock sucked CO2 out of the atmosphere, chilling the planet.

First known Terrestrial Impact of a Binary Asteroid from a Main Belt Breakup Event

Jens Ormö, Erik Sturkell, Carl Alwmark & Jay Melosh

ABSTRACT: Approximately 470 million years ago one of the largest cosmic catastrophes occurred in our solar system since the accretion of the planets. A 200-km large asteroid was disrupted by a collision in the Main Asteroid Belt, which spawned fragments into Earth crossing orbits. This had tremendous consequences for the meteorite production and cratering rate during several millions of years following the event. The 7.5-km wide Lockne crater, central Sweden, is known to be a member of this family. We here provide evidence that Lockne and its nearby companion, the 0.7-km diameter, contemporaneous, Målingen crater, formed by the impact of a binary, presumably ‘rubble pile’ asteroid. This newly discovered crater doublet provides a unique reference for impacts by combined, and poorly consolidated projectiles, as well as for the development of binary asteroids.

The Österplana 065 fossil meteorite from the Glaskarten 3 bed. The meteorite is 86.52 cm large. It is surrounded by a grey reduction halo, in the otherwise red limestone. Oxygen was consumed when the meteorite weathered on the sea floor. The coin in the image has a diameter of 2.5 cm.. Credit: Image courtesy of Lund University.

Paleogeography of Baltica and neighboring cratons at the time of the increased cosmic bombardment following the ~470 Ma asteroid breakup event illustrating the resulting known craters (red dots). Clearwater East is dated to this event (~460–470 Ma). Light blue color represents areas of shallow epicontinental seas, and dark blue areas of deep ocean. This distribution may, however, have varied somewhat due to periodical transgressions and regressions of the sea. The timeline documents the related meteorite falls (black dot and line).

The red dot represents the approximate area of the possible multiple impact in the late Ordovician Period.
The red dot represents the approximate area of the Pilot Lake impact 445 million years ago in the Ordovician Period. At that time CO2 was at 17 times that of present levels and the first terrestrial moss-type (bryophyte) fossils appear.

North American Middle Ordovician impact craters. Key: 1: Ames crater, 2: Decorah crater, 3: Rock Elm Impact Structure, Wisconsin, 4: Slate Islands, Ontario.The Ordovician–Silurian extinction event, the Ordovician extinction, was the second-largest of the five major extinction events in Earth’s history in terms of percentage of genera that went extinct and second largest overall in the overall loss of life. This was the second biggest extinction of marine life, ranking only below the Permian extinction. At the time, all known life was confined to the seas and oceans. More than 60% of marine invertebrates died including two-thirds of all brachiopod (hard upper/lower shells) and bryozoan (aquatic invertebrates) families.

Evidence for Impact: The Ordovician meteor event is a proposed shower of L chondrite meteors that occurred during the Middle Ordovician period, roughly 470 million years ago. This theory was proposed by Swiss and Swedish researchers based on the comparatively tight age clustering of L chondrite grains in sediments in southern Sweden.[1][2][3] They proposed that a large asteroid transferred directly into a resonant orbit with Jupiter, which shifted its orbit to intercept Earth. In addition to the northern European evidence, there is circumstantial evidence that several Middle Ordovician meteors fell roughly simultaneously 469 million years ago in a line across North America, including the Decorah crater in Iowa, the Slate Islands crater in Lake Superior, and the Rock Elm crater in Wisconsin.[4]

References

1. Heck, Philipp; Birger Schmitz, Heinrich Baur, Alex N. Halliday. Rainer Wieler (15). “Fast delivery of meteorites to Earth after a major asteroid collision”. Nature 430: 323-325.

2. H. Haack et al. Meteorite, asteroidal, and theoretical constraints on the 500-Ma disruption of the L chondrite parent body, Icarus, Vol. 119, p. 182 (1996).

3. Korochantseva et al. “L-chondrite asteroid breakup tied to Ordovician meteorite shower by multiple isochron 40Ar-39Ar dating” Meteoritics & Planetary Science 42, 1, pp. 3-150, Jan. 2007.

4. Vastag, Brian (18 February 2013). “Crater found in Iowa points to asteroid break-up 470 million years ago”. Washington Post. Retrieved 19 February 2013.


9. SILURIAN: 443 – 416 MILLION

  • Ordovician–Silurian extinction event 60% of marine genera wiped out;
  • O2 70 % of modern level;
  • mean surface temperature 3 °C above modern level;
  • sea level 180m above present day with short-term negative excursions (glacial cause);
  • Euramerica forms as Gondwana drifts north
  • Wide shallow seas as Ordovician glaciers melt
  • Warm, greenhouse climate
  • Most land is barren, lifeless desert
  • Life begins to creep onto land – primitive plants, ferns
    fungi and myriapoda lead the way, the age of Arthropods.
Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Slate Islands, Lake Superior 32 436 Ma ± 3 Ar40-Ar39 melt rock CONFIRMED Complex Pseudotachylite dating
High Rock Lake, Manitoba ~5 435 ± 10 Geological dating PROBABLE Complex
Lac Couture, Quebec 8 425 ± 25 Ar40-Ar39 melt rock CONFIRMED Complex Submerged central peak
Rock Elm, Wisconsin 6 420–440 Geological dating CONFIRMED Complex Youngest exposed rocks

10. DEVONIAN: 416 – 359.2 MILLION

  • 75% of species lost
  • O2 75 % of modern level;
  • mean surface temperature 6 °C above modern level;
  • sea level 180m above present day gradually falling to 120m;
  • Euramerica and Gondwana drift towards each other;
  • The Age of Fishes and the Invasion of Land;
  • Ocean levels high with wide shallow seas;
  • Warm, greenhouse climate;
  • Late Devonian extinction  – all placodermi (armoured prehistoric fish), and trilobites die off.
Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Franktown structure, Ontario ~2 >400 Ordovician sediment cover PROPOSED Simple Circular depression
Lac La Moinerie, Quebec 8 400 ± 50 Ar40-Ar39 melt rock CONFIRMED Complex
Brent, Ontario 3.8 396 ± 20 K-Ar studies on the coarsely crystalline melt rocks CONFIRMED Simple Overflight of Brent Crater
Elbow, Alberta 8 395 ± 25 Geological dating CONFIRMED Complex Brecciated Devonian strata
Nicholson Lake, North West Territories 12.5 389 ± 6.7 Pb/U CONFIRMED Complex The large island within the lake is the eroded central peak
Flynn Creek, Tennessee ~3.8 382.03 ± 21 Geological dating CONFIRMED Complex Shattercones
Panther Mountain, New York state 10 ~375 Geological dating PROBABLE Complex Inverted relief

 


11. ~374 Ma – LATE DEVONIAN EXTINCTION

75% of species lost — Trilobite, 5 cm length

Trilobites were the most diverse and abundant of the animals that appeared in the Cambrian explosion 550 million years ago. Their great success was helped by their spiky armour and multifaceted eyes. They survived the first great extinction but were nearly wiped out in the second. The likely culprit was the newly evolved land plants that emerged, covering the planet during the Devonian period. Their deep roots stirred up the earth, releasing nutrients into the ocean. This might have triggered algal blooms which sucked oxygen out of the water, suffocating bottom dwellers like the trilobites.

The red dot represents the approximate area of impacts >350 million years ago in the Carboniferous Period.

The Devonian extinction had severe global effects. With a worldwide loss of 60% of existing taxa, every ecosystem was affected. Reef systems were forever changed with the massive deaths of stromatoporoids and tabulate corals. Brachiopods lost their stronghold as the dominant shelled marine invertebrate. Entire classes, such as the agnathan fishes, went extinct. From the loss of microscopic plankton to terrestrial plants, all life on Earth was affected by this major extinction event.Asteroid impacts have become a popular theory examined at extinction events. McLaren (1970) proposed the first bolide-induced extinction for the Late Devonian. To be a single impact, studies have shown that the asteroid would need a diameter greater than ten kilometers. If an asteroid of those proportions impacted earth, it would kill life in the target area, generate earthquakes, tsunamis, wildfires and ballistic molten debris. Tsunamis, especially, would affect shallow marine ecosystems. The blast would heat the atmosphere sufficiently so that nitrogen could combine with oxygen to create nitric oxide and nitric acid. Rain falling in high concentrations could poison upper surface waters and destroy phytoplanktonic life. Calcareous shells would dissolve. Wildfires would produce dioxins and aromatic hydrocarbons, poisoning the environment. Significant addition of carbon dioxide into the atmosphere would create an icehouse effect. Global dust clouds could block sunlight, making photosynthesis impossible. Temperatures could drop below survivable ranges for many organisms.

Evidence for Impact: The Siljan Ring in Sweden, dated to the F-F boundary, has a diameter of 52 kilometers. Many craters have been studied for the Late Devonian extinction event (table), however the dates of many craters are either too wide to be accepted or dates too uncertain based on differing opinions. Larger craters might have been created in the ocean floor, but would now be destroyed by tectonics (McGhee, 1996). Others doubt a single asteroid impact could be responsible for such a severe extinction event.

References

McGhee GR Jr. 1996. The Late Devonian Mass Extinction. New York: Columbia University Press.

McLaren, D.J. 1970. Time, life and boundaries. Journal of Paleontology, 48,. 801–815.


12. MISSISSIPPIAN: 359.2 – 318 MILLION

    • Epoch opens in slow mass extinction, life soon recovers, the age of  amphibians;
    • Euramerica & Gondwana continue to merge; much mountain building; other continent fragments drift closer;
    • Vast forests and swamps form as sea levels fluctuate;
    • Climate hot & humid but glaciated at the poles
    • Oxygen level 40% above today – abundant wildfires
    • amphibious tetrapods multiply wildly; many grow enormous in the high humidity and oxygen;
    • Sea life dominated by sharks, corals, bryozoa,brachiopods, ammonoids, crinoids and foraminifera;
    • much of the world’s coal formed in the Carboniferous
    • Carboniferous Period lasted from about 359.2 to 299 million years ago.
Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Crooked Creek, Missouri ~7 ~348 – 323 Geological dating CONFIRMED Complex Serial impact event?
Charlevoix, Quebec 54 342 ± 15 K-Ar CONFIRMED Peak ring Elevated Earthquake Zone
Weaubleau, Missouri 19 320 – 340 Geological dating PROBABLE Complex Ring-like drainages

13. PENNSYLVANIAN: 318 – 299 MILLION

300 million years ago, the landmass Laurentia collided with Baltica. The Appalachian mountains of eastern North America rose along the edges of the supercontinent, Pangea, and a climate shift thrust the Earth into an ice age. Map courtesy of CR Scotese, PALEOMAP Project
  • Pangea supercontinent forms as all continents collide – significant mountain building worldwide;
  • High sea levels form broad, shallow continental seas and vast coal swamps;
  • Climate hot & humid but glaciated at the poles;
  • Oxygen level 40% above today – abundant wildfires;
  • Much of the world’s coal formed in the Carboniferous;
  • Reptiles appear and diversify wildly; first ancestor of mammals appears.

 

Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Ile Rouleau, Quebec 4 <300 Geological dating CONFIRMED Complex Age based on stratigraphy
Middlesboro, Kentucky 6 <300 Geological dating CONFIRMED Complex Dates to the formation of the supercontinent Pangaea 300 million years ago

14. PERMIAN: 299 – 252.2 MILLION

  • 96% of species lost
  • Pangea supercontinent combines all major landmasses
  • Panthalassa combines all oceans except Tethys
  • Climate swings widely between hot and cold extremes
  • Huge deserts – Carboniferous swamp forests dry up;
  • Egg-laying reptiles (Sauropsids) and mammal-like reptiles (Synapsids) wildly proliferate over the land;
  • Paleozoic Era ends with Permian Mass Extinction – worst in earth’s history with 95% of all life destroyed.
The Permian is a geologic period and system which extends from 298.9 ± 0.2 to 252.2 ± 0.5 (Million years ago). The Permian–Triassic (P–Tr or P–T) extinction event formed the boundary between the Paleozoic and Mesozoic eras. It is the Earth’s most severe known extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct.
Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Clearwater West, Quebec 32 290 ± 20 K-Ar melt rocks CONFIRMED Peak ring  Maskelynite
Des Plaines, Illinois 8 <280 Geological dating CONFIRMED Complex
Douglas, Wyoming ~0.08 ~280 Sedimentological boundary PROPOSED Simple Multiple Strewn Field
Decaturville Structure, Missouri 5.5 260-323 Geological dating CONFIRMED Complex

15. 252.28 Ma – PERMIAN-TRIASSIC EXTINCTION

Permian–Triassic (P–Tr or P–T) – 251.88 (+/- 0.031) million years ago:

Coincidental with the P-Tr extinction, about 2.6 million km2 of 4 km thick basaltic lava covered Siberia in a flood basalt event. The original volume of lava is estimated to range from 1 to 4 million km3 (Wikipedia).
It is unclear whether this magmatism was the main culprit, or simply an accessory to the P-Tr mass extinction.

The Siberian Traps, a deadly epoch of 2.6-million-square-kilometer, 4-kilometer-thick volcanic eruption, left its fingerprint in Siberia and was synchronous with the Permian–Triassic (P-Tr) boundary extinction.

96% of species lost — Tabulate coral, 5 CM

Known as “the great dying”, this was by far the worst extinction event ever seen; it nearly ended life on Earth. The tabulate corals were lost in this period – today’s corals are an entirely different group. What caused it? A perfect storm of natural catastrophes. A cataclysmic eruption near Siberia blasted CO2 into the atmosphere. Methanogenic bacteria responded by belching out methane, a potent greenhouse gas. Global temperatures surged while oceans acidified and stagnated, belching poisonous hydrogen sulfide.  “It set life back 300 million years,” says Schmidt. Rocks after this period record no coral reefs or coal deposits.

 

The red dot represents the approximate area of the Gow impact 250 million years ago at the time of the Permian–Triassic (P–Tr) extinction event.

The Permian–Triassic (P–Tr) extinction event, informally known as the Great Dying, was an extinction event that occurred 252.28 Ma (million years) ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras. It is the Earth’s most severe known extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct. It is the only known mass extinction of insects. Some 57% of all families and 83% of all genera became extinct. Because so much biodiversity was lost, the recovery of life on Earth took significantly longer than after any other extinction event, possibly up to 10 million years (Wikipedia).

Evidence for Impact: Reported evidence for an impact event from the P–Tr boundary level includes rare grains of shocked quartz in Australia and Antarctica; fullerenes trapping extraterrestrial noble gases; meteorite fragments in Antarctica; and grains rich in iron, nickel and silicon, which may have been created by an impact. However, the accuracy of most of these claims has been challenged. Quartz from Graphite Peak in Antarctica, for example, once considered “shocked”, has been re-examined by optical and transmission electron microscopy. The observed features were concluded to be not due to shock, but rather to plastic deformation, consistent with formation in a tectonic environment such as volcanism. An impact crater on the seafloor would be a possible cause of the P–Tr extinction, and such a crater would by now have disappeared. As 70% of the Earth’s surface is sea, an asteroid or comet fragment is more than twice as likely to hit ocean as it is to hit land. However, Earth has no ocean-floor crust more than 200 million years old, because the “conveyor belt” process of seafloor spreading and subduction destroys it within that time. Craters produced by very large impacts may be masked by extensive flood basalting from below after the crust is punctured or weakened. Subduction should not, however, be entirely accepted as an explanation of why no firm evidence can be found: as with the K-T event, an ejecta blanket stratum rich in siderophilic elements (e.g., iridium) would be expected to be seen in formations from the time. One attraction of large impact theories is that theoretically they could trigger other cause-considered extinction-paralleling phenomena, such as the Siberian Traps eruptions as being either an impact site or the antipode of an impact site. The abruptness of an impact also explains why more species did not rapidly evolve to survive, as would be expected if the Permian-Triassic event had been slower and less global than a meteorite impact (Wikipedia).


16. TRIASSIC: 252.2 – 199.6 MILLION

 

200 million years ago, dinosaurs roamed the supercontinent Pangea, surrounded by the Panthalassic Ocean, the oceanic ancestor of the Pacific Ocean.
  • 80% of species lost
  • Pangea supercontinent combines all major landmasses;
  • Panthalassa combines all oceans except Tethys;
  • Climate very hot and dry with huge deserts;
  • Archosaurs wildly diversify, becoming the crocodilian Crurotarsi, the flying Pterosaurs, and Dinosaurs;
  • Dinosaurs originated (around 230 million years ago) in South America,  Pangea;
  • Marine reptiles  flourish;
  • Gymnosperm trees (conifers, ginkos; cycads) thrive;
  • Turtles, modern amphibians, modern fish, modern corals and many modern insect groups appear;
  • the Manicouagan impact may possibly have triggered an earlier mass extinction at the Carnian/Norian boundary 227 Ma, in the Late Triassic.
  • Period ends in large extinction.

The Triassic is a geologic period and system that extends from about 250 to 200 Ma (252.2 ± 0.5 to 201.3 ± 0.2) million years ago).

Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Gow, Saskatchewan 5 <250 Radioactive decay CONFIRMED Complex Smallest currently known complex
St. Martin, Manitoba ~40 227.8 ±0.9 Ar40-Ar39 melt rock CONFIRMED Complex Maskelynite – Dauphin River diversion?
Manicouagan, Quebec 100 214 ± 1 Zircon/melt rock dating CONFIRMED Peak ring basin Maskelynite
Red Wing, North Dakota 9.1 200 ± 25 Geological dating CONFIRMED Complex? Stratigraphy
Wells Creek, Tennessee ~12 200 ± 100 Geological dating CONFIRMED Complex Shattercones

17. ~214 Ma – LATE TRIASSIC (extinction at the Carnian/Norian boundary – 227 Ma)

80% of species lost — Conodont teeth 1 mm

Palaeontologists were baffled about the origin of these toothy fragments, mistaking them for bits of clams or sponges. But the discovery of an intact fossil in Scotland in the 1980s finally revealed their owner – a jawless eel-like vertebrate named the conodont which boasted this remarkable set of teeth lining its mouth and throat. They were one of the first structures built from hydroxyapatite, a calcium-rich mineral that remains  a key component of our own bones and teeth today.  Of all the great extinctions, the one that ended the Triassic is the most enigmatic. No clear cause has been found.

Scientists reported in the journal Nature today (March 13, 1998) that they had found evidence of a chain of five craters formed 214 million years ago that was likely due to pieces of a comet crashing into the Earth’s surface, similar to the Comet Shoemaker-Levy 9 impact on Jupiter in 1994. The craters no longer appear to be in a straight line due the shifting of the Earth’s continents due to plate tectonics. Two of the craters, Manicouagan and Saint Martin, are in Canada (Quebec and Manitoba, respectively). The other three craters are Rochechouart in Europe, Obolon in the Ukraine and Red Wing in Minnesota. The impacts appeared to occur at the Norian stage of the Triassic period, about six million years after a mass extinction that wiped out 80% of all the species on Earth, but the ages of all the craters are uncertain enough to include this extinction (from ScienceWeb Daily).

Abstract:

The 34-million-year (My) interval of the Late Triassic is marked by the formation of several large impact structures on Earth. Late Triassic impact events have been considered a factor in biotic extinction events in the Late Triassic (e.g., end-Triassic extinction event), but this scenario remains controversial because of a lack of stratigraphic records of ejecta deposits. Here, we report evidence for an impact event (platinum group elements anomaly with nickel-rich magnetite and microspherules) from the middle Norian (Upper Triassic) deep-sea sediment in Japan. This includes anomalously high abundances of iridium, up to 41.5 parts per billion (ppb), in the ejecta deposit, which suggests that the iridiumenriched ejecta layers of the Late Triassic may be found on a global scale. The ejecta deposit is constrained by microfossils that suggest correlation with the 215.5-Mya, 100-km-wide Manicouagan impact crater in Canada. Our analysis of radiolarians shows no evidence of a mass extinction event across the impact event horizon, and no contemporaneous faunal turnover is seen in other marine planktons. However, such an event has been reported among marine faunas and terrestrial tetrapods and floras in North America. We, therefore, suggest that the Manicouagan impact triggered the extinction of terrestrial and marine organisms near the impact site but not within the pelagic marine realm (Onoue, Tetsuji, October 2012).

Summary of impact structures in the Late Triassic.

A) Map showing the palaeo-position and distribution of the Central Atlantic Magmatic Province (CAMP) and the studied sections in the US, Morocco and UK in pre-drift position for the end-Triassic. B) Summary of the correlation-tools used to correlate the terrestrial and marine sections. Main events recognized in the different sections are shown in italic. GPTS: Geomagnetic Polarity Time Scale.

Did the Manicouagan impact trigger end-of-Triassic mass extinction?

J. P. Hodych, G. R. Dunning
Abstract
We use U-Pb zircon dating to test whether the bolide impact that created the Manicouagan crater of Quebec also triggered mass extinction at the Triassic/Jurassic boundary. The age of the impact is provided by zircons from the impact melt rock on the crater floor; we show that the zircons yield a U-Pb age of 214 ±1 Ma. The age of the Triassic/Jurassic boundary is provided by zircons from the North Mountain Basalt of the Newark Supergroup of Nova Scotia; the zircons yield a U-Pb age of 202 ±1 Ma. This should be the age of the end-of-Triassic mass extinction that paleontology and sedimentation rates suggest occurred less than 1 m.y. before extrusion of the North Mountain Basalt. Although the Manicouagan impact could thus not have triggered the mass extinction at the Triassic/Jurassic boundary (impact likely having preceded extinction by 12 ±2 m.y.), the impact may possibly have triggered an earlier mass extinction at the Carnian/Norian boundary – 227Ma, in the Late Triassic. (Geology (1992)

The Triassic-Jurassic Extinction – Volcanic? 

The end-Triassic mass extinction, with more than 50% genus loss in both marine and continental realms, is one of the five periods of major biodiversity loss in Earth’s history and provides an eminent case history of global biosphere turnover. Massive volcanism through largescale flood basalt eruptions is the favoured terrestrial culprit. The end-Triassic is marked by Large Igneous Province (LIP) emplacement of the Central Atlantic Magmatic Province (CAMP). Deenen et al, 2009.

References

Boyle, D.R. et al, Geochemistry, geology, and isotopic (Sr, S, and B) composition of evaporites in the Lake St. Martin impact structure: New constraints on the age of melt rock formation,GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, VOL. 8, 2007.

M.H.L. Deenen, M. Ruhl, N.R. Bonis,W. Krijgsman, W.M. Kuerschner, M. Reitsma, M.J. van Bergen, A new chronology for the end-Triassic mass extinction. Earth and Planetary Science Letters 2009.

Donofrio, R.R., North American impact structures hold giant field potential. Oil and Gas Journal, 1998.

Donofrio, R.R.: Impact Craters: Implications for Basement Hydrocarbon Production. Journal of Petroleum Geology, 1981.

Grieve, R.A.F., Impact structures in Canada, Geological Association of Canada, no. 5, 2006.

Robertson, P.B., Grieve, R.A.F., Impact Structures in Canada: their recognition and characteristics. The Journal of the Royal Astronomical Society, February 1975.

Smith, R. Dark days of the Triassic: Lost world – Did a giant impact 200 million years ago trigger a mass extinction and pave the way for the dinosaurs? NATURE 17 Nov. Vol#479 2011.

Tetsuji Onouea, et al; Deep-sea record of impact apparently unrelated to mass extinction in the Late Triassic. Rutgers University/Lamont-Doherty Earth Observatory, Palisades, NY, October 3, 2012

Poag C. W, Chesapeake Invader, 1999.

Earth Impact Database


18. 201.3 Ma – TRIASSIC-JURASSIC EXTINCTION

The following impacts “may” be related to the Triassic–Jurassic Extinction:

The red dot represents the approximate area of the Red Wing impact approximately 200 million years ago in the Triassic Period.
The red dot represents the approximate area of the Viewfield impact 190 million years ago in the Jurassic Period.

The Triassic–Jurassic extinction event marks the boundary between the Triassic and Jurassic periods, 201.3 million years ago, and is one of the major extinction events of the Phanerozoic eon, profoundly affecting life on land and in the oceans. In the seas a whole class (conodonts) and twenty percent of all marine families disappeared. On land, all large crurotarsans (non-dinosaurian archosaurs) other than crocodilians, some remaining therapsids, and many of the large amphibians were wiped out. At least half of the species now known to have been living on Earth at that time went extinct. This event vacated terrestrial ecological niches, allowing the dinosaurs to assume the dominant roles in the Jurassic period. This event happened in less than 10,000 years and occurred just before Pangaea started to break apart. In the area of Tübingen (Germany), a Triassic-Jurassic bonebed can be found, which is characteristic for this boundary. Statistical analysis of marine losses at this time suggests that the decrease in diversity was caused more by a decrease in speciation than by an increase in extinctions (Wikipedia).

Evidence for Impact: “Analysis of tetrapod footprints and skeletal material from more than 70 localities in eastern North America shows that large theropod dinosaurs appeared less than 10,000 years after the Triassic-Jurassic boundary and less than 30,000 years after the last Triassic taxa, synchronous with a terrestrial mass extinction. This extraordinary turnover is associated with an iridium anomaly (up to 285 parts per trillion, with an average maximum of 141 parts per trillion) and a fern spore spike, suggesting that a bolide impact was the cause. Eastern North American dinosaurian diversity reached a stable maximum less than 100,000 years after the boundary, marking the establishment of dinosaur-dominated communities that prevailed for the next 135 million years” (Olsen et al 2002).

P. E. Olsen, D. V. Kent, H.-D. Sues, C. Koeberl, H. Huber, A. Montanari, E. C. Rainforth, S. J. Fowell, M. J. Szajna, B. W. Hartline ASCENT OF DINOSAURS LINKED TO AN IRIDIUM ANOMALY AT THE TRIASSIC JURASSIC BOUNDARY Science, 17 May 2002


19. DINOSAUR  EVOLUTION AT THE END-TRIASSIC (Tr-J) vs END-CRETACEOUS (K-Pg) EXTINCTIONS

  • INTRODUCTION
  • K-Pg & Tr-J GEOMORPHOMETRY COMPARISONS
    – IMPACT CRATERS
    – IMPACT EJECTA
    – IRIDIUM CONCENTRATIONS
    – VOLCANIC ACTIVITY
    – CLIMATE CHANGE
  • CONCLUSION
  • REFERENCES
    – PAPERS
    – CONTINENTAL DRIFT vs GEOLOGIC PERIODS
    – MANICOUAGAN and CHICXULUB CRATER DATA SUMMARY

– INTRODUCTION

The direct ancestors of the dinosaurs (early Archosaurs)  and mammal-like reptiles (Therapsids) originated within 10 million years of each other within the Triassic Period of the Mesozoic Era. They co-existed for some 30 million years along with the reptilian ancestors of modern-day crocodiles. The reptiles with diverse body types were more successful than early dinosaurs and mammals during this time.

At the End Triassic (Tr-J) extinction, the crocodile relatives (reptiles) were almost completely gone and the dinosaurs began their 135 million-year domination on our planet.

“Stiff Competition: For much of the Triassic period dinosaurs (and mammals) were a marginal group, overshadowed by the likes of crocodile relatives such as Saurosuchus (1) and giant amphibians such as Metoposaurus (2). Credit: Ricardo N. Martínez Institute and Museum of Natural Sciences, National University of San Juan (1); Tomasz Sulej Institute of Paleobiology, Polish Academy of Sciences (2)” (Scientific American May 2018)

 

Phytosaurs are an extinct group of large, mostly semiaquatic Late Triassic archosauriform reptiles. Phytosaurs belong to the family Phytosauridae and the order Phytosauria (dinosaur predators).

After the Cretaceous-Paleogene (K–Pg) extinction 66 million-years-ago, the non-avian dinosaurs were completely gone and mammals began their domination of our planet.

This artist’s rendering of the hypothetical placental ancestor – the Common Ancestor of all Placental Mammals – was surviving in the Tertiary environment of 65 million years ago. With the demise of their dinosaur predators, mammal evolution accelerated. (Image courtesy of Carl Buell)
The following physical, chemical and biological alterations occurred on our planet  during the Tr-J and the K-Pg extinctions:
  • IMPACT CRATERS:  an approximately circular depression in the surface of a planet, moon, or other solid body in the Solar System or elsewhere, formed by the hypervelocity (>12km/sec) impact of a smaller body.
  • IMPACT EJECTA: a special group of sediments comprising material that is thrown out from an impact crater in the excavation stage and deposited at a distance determined by the size of the impact.
  • IRIDIUM (Ir) CONCENTRATIONS: “Iridium is one of the rarest elements existing in two parts per billion in the Earth’s crust. Iron meteorites contain about 3 parts per million of iridium. Stony meteorites contain about 0.64 parts per million of iridium” (Chemistry Explained).
  • VOLCANIC ACTIVITY: “In geology, a large igneous province (LIP) is an extremely large accumulation of igneous rocks, including plutonic rocks (intrusive) or volcanic rock formations (extrusive), arising when hot magma extrudes from inside the Earth and flows out. The source of many or all LIPs is variously attributed to mantle plumes or to processes associated with plate tectonics (Foulger 2010)”. Traps, the Swedish word for stairs, refers to the stepped appearance of lava flows that oozed from a vast rift in the Earth’s crust for nearly a million years.
  • CLIMATE CHANGE: a change in the statistical properties (principally its mean and spread) of the climate system when considered over long periods of time, regardless of cause.

The K-Pg extinction that ended the non-avian dinosaurs is well explained. But there is a mystery of how the reptiles lost their domination at the Tr-J extinction allowing the dinosaurs to dominate.

My article documents the influence the two separate extinctions had on the physical, chemical and biological alterations on our planet and their common characteristics.

– K-Pg & Tr-J  GEOMORPHOMETRY COMPARISONS

CRETACEOUS-PALEOGENE (K–Pg) – 66.043 ± 0.011 million-years-ago:

  • IMPACT CRATER:
“The K–Pg extinction event, a sudden mass extinction of some three-quarters of the plant and animal species on Earth, was caused by a large bolide impact. In 1990 Hildebrand et al. showed that the source crater for the K-Pg extinction is probably the 180-km-diameter Chicxulub crater which lies on the Yucatan Peninsula, Mexico. Non-avian dinosaurs did not survive this event” (Hildebrand 1993).
“Knowing the size and location of the crater allows well-constrained modelling of the lethal effects of the impact. The Chicxulub impact produced a massive pulse of shock-devolatized CO2 and SO2 because the target rocks included a thick sequence of carbonates and sulphates. It was therefore particularly lethal for an impact of its size” (Hildebrand 1993).
The Chicxulub Impact Crater is illustrated here immediately over the horizon . I took this image during a cruise just to the east of the impact site. I stood on my tippy-toes to try and get the crater over the horizon only to be photo-bombed by a whale. If I was at this location 65 million years ago during the impact, either the extreme heat shock wave of asteroid atmosphere contact/entry, or the impact explosion or the tsunami hundreds of metres high would have made a very bad day for me.
  •  IMPACT EJECTA:

“The K-Pg boundary clay is known to consist of two layers:
– a globally-distributed, uniform ~3-mm-thick layer which was probably dispersed by the impact fireball and
– a layer found only near the source crater composed of ballistically-distributed ejecta.
Chondritic siderophile trace -element anomalies, shocked minerals and tektites have been subsequently found in the K-Pg boundary layers” (Hildebrand 1993).

br Close-up of the Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K–T) boundary – at the Royal Tyrrell Museum, Drumheller Alberta. (Image by the author)
  • IRIDIUM (Ir) CONCENTRATIONS:

“The mass of the Chicxulub asteroid is calculated to be about 300 billion metric tons with an asteroid diameter 10 ± 4 kilometers (km), determined from the iridium measurements in the K-Pg boundary (about 100 times natural concentrations), the concentration of iridium in so-called chondritic meteorites and the surface area of the Earth, ” (Alverez 1997).

“THE IRIDIUM ANOMALY: The levels of iridium across the Gubbio formation are plotted. Note the spike in the K-T boundary clay.” (Alverez)
  • VOLCANIC ACTIVITY:

The Deccan Traps began forming 66.25 million years ago at the end of the Cretaceous period. This series of eruptions may have lasted less than 30,000 years in total.

The lava flows covered 1.5 million km2 of  western India with multiple layers of solidified flood basalt more than 2,000 m thick. The Deccan Traps region was reduced to its current size by erosion and plate tectonics; the present area of directly observable lava flows is around 500,000 km2.

The Chicxulub asteroid impact and the eruption of the massive Deccan volcanic province are two proposed causes of the end-Cretaceous mass extinction, which includes the demise of nonavian dinosaurs.

“U-Pb zircon geochronology of Deccan rocks show that the main phase of eruptions initiated ~250,000 years before  and continued for 500,000 years after the Cretaceous-Paleogene boundary.  More than 1.1 million km3 of basalt erupted in those ~750,000 years. The Deccan Traps contributed to the latest Cretaceous environmental change and biologic turnover that culminated in the marine and terrestrial mass extinctions.” (Schoene 2015)

“There is evidence for the triggering of magmatism on a global scale by the Chicxulub meteorite impact at the Cretaceous-Paleogene (K-Pg) boundary, recorded by transiently increased crustal production at mid-ocean ridges. Concentrated positive free-air gravity and coincident seafloor topographic anomalies, associated with seafloor created at fast-spreading rates, suggest volumes of excess magmatism in the range of ~105 to 106 km3. Widespread mobilization of existing mantle melt by post-impact seismic radiation can explain the volume and distribution of the anomalous crust. This massive but short-lived pulse of marine magmatism should be considered alongside the Chicxulub impact and Deccan Traps as a contributor to geochemical anomalies and environmental changes at K-Pg time.” (Byrnes 2018)

“Part of the Deccan Traps in western India with 1000 Km igneous rock deposition (layers)” (Wikipedia / Nichalp}.
  • CLIMATE CHANGE:

“The Chicxulub impact produced a massive pulse of shock-devolatized CO2 and SO2 because the target rocks included a thick sequence of carbonates and sulphates and was therefore particularly lethal for an impact of its size. The addition of these gases to the atmosphere led to a global sulphurous acid rain and a long-term CO2 greenhouse warming of ~10° Celsius. The Chicxulub impact was orders of magnitude more deadly to the environment than any known terrestrial process such as volcanism. Extinction-causing impacts of this size reoccur approximately once every 100 million years thereby altering the long-term evolution of life on earth” (Hildebrand 1993).

TRIASSIC-JURASSIC (Tr-J) –  237-201.3 million-years-ago:

  • IMPACT CRATERS: 
Dated within the 237-201.3 million-year time frame of the End Triassic, many large bolide impacts have been identified at present-day northern latitudes. They range from 9 to >100 km in diameter.

The presence of impact structures with Late Triassic ages suggests the possibility of bolide impact-induced environmental degradation prior to the end-Triassic.

M = Manicouagan (215.5 Ma; 100 km diameter); SM = Saint Martin (227.8 Ma; 40 km diameter); R = Rochechouart (ca. 207–201 Ma; ca. 23–50 km diameter); RW = Red Wing structure (ca. 200 Ma; 9.1 km diameter, ca. 2.5 km burial depth); P = Paasselkä (231 Ma; 9 km diameter); not illustrated – Puchezh_Katunki (167 Ma; 40 km diameter); not illustrated –  Obolon (169 Ma; 20 km diameter).

“The attempts to establish a globally significant causal extinction connection between the larger impacts (e.g. Manicouagan and Rochechouart) and Late Triassic marine and terrestrial bioevents (culminating with the End Triassic Extinction), have proved unsuccessful” (Clutson et al 2018).

The Manicouagan impact crater looking east as seen from GOZooM. At this distance seeing the crater for the first time, I was “impressed” by the size of this structure. Image by the author from C-GOZM.
The Dauphin river is illustrated paralleling the northern rim of the St. Martin impact structure as it flows into Lake Winnipeg. Image by the author from C-GOZM.
Red Wing structure – the superimposed circle illustrates the position of the buried crater. This image, aimed looking east at the approximate point of impact, was taken from GO ZooM at approximately 4500 feet AGL. Image by the author from C-GOZM.
  •  IMPACT EJECTA: 

214 Ma – LATE TRIASSIC EJECTA – SW BRITAIN
“The documented late Triassic spherule layer of SW England deposit contains an abundance of spherules, common shocked quartz and a suite of accessory minerals believed to have been derived direct from the impact site. These include garnets, ilmenites, zircons and biotites. Garnets and ilmenites are highly fractured, and biotites show prominent kink bands indicative of shock” (Thackrey 2009) .

“The Late Triassic ejecta deposit of SW Britain where impact melt spherules have been completely altered to clay. Radiogenic dating of this deposit  shocked biotites (observed exclusively in this Late Triassic ejecta deposit) yielded ages consistent with the Grenvillian target rocks at Manicouagan” (Thackrey 2009).
  • IRIDIUM (Ir) CONCENTRATIONS:

“New analyses confirms Ir enrichment (up to 0.31 ng/g) in close proximity to the palynological Triassic–Jurassic boundary in strata near the top of the Blomidon Formation at Partridge Island, Nova Scotia. High Ir concentrations have been found in at least two samples within the uppermost 70 cm of the formation. There is enrichment of some  platinum group elements (including Ir) and transition group elements in strata that occur at, and in close stratigraphic proximity to, the horizon of palynological turnover that is interpreted as the Triassic–Jurassic boundary in the Fundy basin” (Tanner 2005).

Lithostratigraphy of the uppermost meter of the Blomidon Formation and Ir concentrations determined by NAA and ICP-MS analyses. Sample identification numbers demarcate the depth (in centimeters) below the contact with the North Mountain Basalt of the top of the 5-cm sample interval. Ir is plotted as the mid-point of the sample interval. TJB=position of Triassic–Jurassic boundary as determined by palynology [12]. NA=sample not analyzed; BD=concentration below detection limit.
  • VOLCANIC ACTIVITY:

Two volcanic episodes in the Triassic are significant to dinosaur evolution:

1. “The Central Atlantic Magmatic Province (CAMP) is the Earth’s largest continental large igneous province, covering an area of roughly 11 million km2. It is composed mainly of basalt that formed prior to the breakup of Pangaea near the end of the Triassic and the beginning of the Jurassic periods.

The Tr-J multi-sized impact events formed prior to commencement of the CAMP volcanic episode by several million years.

214 Ma – CENTRAL ATLANTIC MAGMATIC PROVINCE (CAMP) and BAY OF FUNDY

Widespread eruptions of flood basalts of the Central Atlantic Magmatic Province (CAMP) were synchronous with or slightly postdate the Late Triassic boundary” (Tanner 2004).

“Location and geologic map of the study area in the Fundy basin. Samples analyzed in this study were collected from Partridge Island, near Parrsboro, Nova Scotia” (Tanner 2005).

“The Bay of Fundy terrestrial redbeds of the Blomidon Formation were deposited during the late Triassic and early Jurrasic. A 10-m-thick zone of intensely deformed strata that occurs near the base of the formation is characterized by faulting. Correlation of this zone basin-wide indicates that it is a record of a very powerful paleoseismic event. The presence in strata just above the deformed zone of quartz grains displaying features of shock metamorphism raises the intriguing possibility that reactivation of the fault zone was triggered by a bolide impact” (Tanner 2002).

Cape Split Bay of Fundy, Nova Scotia, the craggy escarpment which rings this immense gulf was formed during a critical juncture in Earth history called the Triassic-Jurassic boundary, 200 million years ago (Thurston, 1994). The uppermost meter of the Blomidon Formation within this escarpment contains irridium (Ir) concentrations possibly from the Manicouagan impact. Image by the author from C-GOZM.

2. “Wrangellia flood basalts formed as an oceanic variety of a large igneous province (LIP) in the Middle to Late Triassic, with accretion to western North America occurring in the Late Jurassic or Early Cretaceous” (Richards et al., 1991).

The accreted Wrangellia oceanic plateau in the Pacific Northwest of North America is perhaps the most extensive accreted remnant of an oceanic plateau in the world where parts of the entire volcanic stratigraphy are exposed.
Prince Rupert, British Columbia, illustrating the mountains, in the background looking north, created by the collision of the Wrangellia igneous province with Canada’s west coast. The Carnian Pluvial Episode (CPE) contemporaneous with this event is coincidental with the rise of the dinosaurs in the late Triassic. Image by the author from C-GOZM.
  • CLIMATE CHANGE:

“The dinosaurs had a sudden growth in size at the of the end of the Carnian Pluvial Episode (CPE) in the Triassic period. This was a time when climates shuttled from dry to humid and back to dry again.

“At the CPE, the massive eruptions in western Canada, represented today by the great Wrangellia basalts, caused bursts of global warming, acid rain, and killing/extinctions on land and in the oceans”  (Bernardi 2018).

It is suspected that the Wrangellia had a telling effect at the CPE and the beginning of the 135 million-year dinosaur domination.

 “THE CORRELATION BETWEEN THE EARLIEST DINOSAUR OCCURRENCES ACROSS PANGAEA. Note the synchronicity of the first dinosaur diversification event during and after the CPE (light green boxes)” (Bernardi 2018).

– CONCLUSION

Cretaceous–Paleogene (K–Pg) – 66.043 ± 0.011 million years ago – the end of the dinosaur era
“Sixty-five million years ago, a comet or asteroid larger than Mount Everest slammed into the Earth, creating the Chicxulub crater, inducing an explosion equivalent to the detonation of a hundred million hydrogen bombs. Vaporized detritus blasted through the atmosphere upon impact, falling back to Earth around the globe. Disastrous environmental consequences ensued: a giant tsunami, continent-scale wildfires, darkness, and cold, followed by sweltering greenhouse heat. When conditions returned to normal, half the plant and animal genera on Earth had perished” (Alverez 1997). The non-avian dinosaurs were now extinct, making way for mammals to evolve and dominate our planet.

Triassic-Jurassic (Tr-J) –  201.3 million years ago: –the beginning of the dinosaur era
For 30 million years primitive dinosaurs and mammals lived alongside giant, crocodile-like animals known as the crurotarsans in the Triassic Period. The reptilian crurotarsans outnumbered the dinosaurs and were even more diverse. At the Triassic–Jurassic boundary 200 million years ago, the reptilian crurotarsans were virtually gone making way for the dinosaurs to evolve and dominate our planet.

Closing argument:

Dinosaurs originated about 245 Ma, during the recovery from the Permian-Triassic mass extinction. They remained insignificant until they emerged in diversity and ecological importance during the Late Triassic Tr-J event, 201 million years ago. Thus began the 135-million-year dinosaur domination of our planet.

At the K-Pg 66 million years ago, a bolide impact ended the reign of the non-avian dinosaurs.

The geomorphometry of the K-Pg and Tr-J events were compared to illustrate their similarities.

“However, the mode and timing of the origin and diversification of the dinosaurs at the Tr-J have so far been unresolved” (Bernardi 2018).

“There is serious debate on whether the ETE actually exists, or whether it was an event that was attenuated over ~40 Ma (almost 2/3 the time span of the Tertiary!)”(David E. Brown – private correspondence 2018).

“The K/T (K/Pg) impact at the End Cretaceous, turned the Earth’s surface into a living hell, a dark, burning, sulphurous world where all the rules governing survival of the fittest changed in minutes. The dinosaurs never had a chance” (Hildebrand 1993). “Accelerated biotic turnover during the LateTriassic has led to the perception of an End-Triassic mass extinction event, now regarded as one of the ‘‘big five’’ extinctions” (Tanner 2004).

– REFERENCES

  • PAPERS

Walter Alvarez  T. rex and the Crater of Doom  University of California, Berkeley (1997)

Massimo Bernardi, et al  Dinosaur diversification linked with the Carnian Pluvial Episode Nature Communications volume 9 (2018)

Stephen Brusatte The Unlikely Triumph of Dinosaurs Scientific American (May 2008)

Joseph S. Byrnes and Leif Karlstrom Anomalous K-Pg–aged seafloor attributed to impact-induced mid-ocean ridge magmatism Science Advances  (07 Feb 2018)

Hildebrand and Boynton, Proximal Cretaceous-Tertiary boundary impact deposits in the Caribbean. Science, 248 (1990)

Clutson, M.J., Brown, D.E., and Tanner, L.H., 2018 Distal Processes and Effects of Multiple Late Triassic Terrestrial Bolide Impacts: Insights from the Norian Manicouagan Event, Northeastern Quebec, Canada In: L.H. Tanner (ed), The Late Triassic World: Earth in a Time of Transition. Topics in Geobiology Vol. 46, Springer, Cham. ISBN: 978-3-319-68008-8 / 978-3-319-68009-5. DOI

Foulger, G.R.  Plates vs. Plumes: A Geological Controversy. Wiley-Blackwell. (2010)

Alan R. Hildebrand, The Cretaceous / Tertiary Boundary Impact – the Dinosaurs Didn’t have a Chance Journal of the Royal Astronomical Society of Canada, (APR, 1993)

Susannah F. Locke Was the Dinosaurs’ Long Reign on Earth a Fluke? Scientific American (Sept 2008)

Charlotte S. Miller, Francien Peterse, Anne-Christine da Silva, Viktória Baranyi,
Gert J. Reichart & Wolfram M. Kürschner Astronomical age constraints and
extinction mechanisms of the Late Triassic Carnian crisis 
SCIENTIFIC REPORTS (2017)

Lucas S.G., Tanner L.H., The Missing Mass Extinction at the Triassic-Jurassic Boundary Program & Abstracts, Northeastern Section of the Geological Society of America 53rd Annual Meeting, Burlington, VT, March 18-20, 2018, Abstract No.310396 (poster).

Tetsuji Onoue, Honami Sato, Daisuke Yamashita, Minoru Ikehara, Kazutaka Yasukawa, Koichiro Fujinaga, Yasuhiro Kato & Atsushi Matsuoka Bolide impact triggered the Late Triassic extinction event in equatorial Panthalassa  SCIENTIFIC REPORTS (2016)

Richards, M. A., Jones, D. L., Duncan, R. A. & DePaolo, D. J. . A mantle plume initiation model for the Wrangellia flood basalt and other oceanic plateaus. Science254, 263-267.(1991)

Blair Schoene, Kyle M. Samperton, Michael P. Eddy, Gerta Keller, Thierry Adatte, Samuel A. Bowring  U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction Science (2015)

Tanner L.H.,Clutson, M.J., Brown, D.E.,   DISTAL EVIDENCE (?) OF THE LATE TRIASSIC (NORIAN) MANICOUAGAN IMPACT, NORTHEASTERN QUEBEC: NEW DATA FROM THE FUNDY GROUP (CANADIAN MARITIMES) Program & Abstracts, Northeastern Section of the Geological Society of America 53rd Annual Meeting, Burlington, VT, March 18-20, 2018, Abstract No.310396 (poster).

L.H. Tanner, SYNSEDIMENTARY SEISMIC DEFORMATION IN THE BLOMIDON FORMATION (NORIAN-HETTANGIAN), FUNDY BASIN, CANADA Department of Biological Sciences,  Le Moyne College, Syracuse, NY (2006)

Lawrence H. Tanner, Frank T. Kyte Anomalous iridium enrichment at the Triassic–Jurassic boundary, Blomidon Formation, Fundy basin, Canada  Department of Biological Sciences,  Le Moyne College, Syracuse, NY (2005)

L.H. Tanner, S.G. Lucasb, M.G. Chapmanc Assessing the record and causes of Late Triassic extinctions Earth-Science Reviews 65 (2004)

Lawrence H. Tanner, STRATIGRAPHIC RECORD IN THE FUNDY RIFT BASIN OF THE MANICOUAGAN IMPACT: BOLIDE WITH A BANG OR A WHIMPER?  Geography and Geosciences, Bloomsburg Univ (2002)

Tanner, L. H.,  Far-reaching seismic effects of the Manicouagan impact: evidence from the Fundy basin. Geological Society of America, Abstracts with Programs, 35 (6), 167. 2003.

L.H. Tanner, Formal definition of the Lower Jurassic McCoy Brook Formation, Fundy Rift Basin, eastern Canada Department of Geography and Earth Science, Bloomsburg University, (1996)

Scott Neil Thackrey, Gordon Mark Walkden, A. Indares, A. Horstwood, S. Kelley, R. Parrish The use of heavy mineral correlation for determining the source of impact ejecta: A Manicouagan distal ejecta case study Earth and Planetary Science Letters (2009.06.010)

Harry Thurston (Author),‎ Stephen Homer (Illustrator) Tidal Life: A Natural History of the Bay of Fundy (1998)


20. JURASSIC: 199.6 – 145.5 MILLION

  • Pangea supercontinent begins to split with significant mountain-building and volcanism;
  • seas fill rift zones, Panthalassa and Tethys oceans begin shrinking;
  • Climate warm and humid with vast tropical forests;
  • The plankton that lived in the Jurassic period made our crude oil;
  • Dinosaurs dominate the land;
  • First birds arise from small dinosaurs;
  • Marine reptiles flourish;
  • Gymnosperm trees form global forests with vast ‘prairies’ of ferns.
The Jurassic  is a geologic period and system that extends from 201.3± 0.6 Ma (million years ago) to 145± 4 Ma.
Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Viewfield, Saskatchewan 2.5 190 ± 20 Geological dating CONFIRMED Simple Jurassic-Triasic post-impact deposit
Cloud Creek, Wyoming 7 ~190 ± 30 Geological dating CONFIRMED Complex Chronostratigraphic
Hartney, Manitoba 6 <190 ± 20 Geological dating PROBABLE Complex? Structurally uplifted centre
Upheaval Dome, Utah 5.5 <170 Geological dating CONFIRMED Complex Younger than the Jurassic Navajo Sandstone

21. CRETACEOUS: 145.5 – 65.5 MILLION

100 million years ago, Pangaea broke apart. The Atlantic Ocean poured in between Africa and the Americas. India broke away from the African continent, and Antarctica and Australia, still connected above sea level, were stranded near the South Pole.
  • Laurasia splits into North America and Eurasia;
  • Gondwana fractures into Africa, South America, Antarctica/Australia, and India (an island continent);
  • Shrinking Panthalassa becomes Pacific Ocean;
  • Atlantic Ocean forms as Tethys continues to shrink;
  • Climate warm and humid world-wide with vast forests;
  • Broad shallow continental seas stabilize temperatures;
  • Dinosaurs – in wide variety – dominate the land;
  • Birds proliferate as pterosaurs decline;
  • Flowering plants (angiosperms) appear & flourish with help from new insects;
  • Calcium-shelled marine life leave vast chalk beds;
  • Era ends when asteroid impact brings mass extinction;
  • Chicxulub impact might have triggered the enormous Poladpur, Ambenali, and Mahabaleshwar (Wai Subgroup) lava flows in the Deccan traps.
The Cretaceous, derived from the Latin “creta” (chalk), usually abbreviated K for its German translation Kreide (chalk), is a geologic period and system from circa 145 ± 4 to 66 Ma (million years ago).

Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Miami Florida Crater/Structure ~1 ~140 After Florida Plateau deposition IMPROBABLE Complex? Underwater off Miami
Hotchkiss Structure, Alberta 3.9 120-330 Dated unconformity PROPOSED Complex Seismic research
Carswell, Alberta 39 115 ± 10 40Ar/39Ar CONFIRMED Peak ring Multi-ring impact?
West Hawk, Manitoba 2.44 100 Geological dating CONFIRMED Simple No reliable age
Deep Bay, Saskatchewan 9.5 99 ± 4 Geological dating CONFIRMED Simple Flat-floored Cretaceous sediments
Kentland, Indiana ~13 >97 Geological dating CONFIRMED Complex Quarry
Steen River Albera 25 91 ± 7 K-Ar pyroclastic vesicular rock CONFIRMED Complex Magnesioferrite MgFe2O
Howell Creek, BC ~10 90-97 Between syenites and Cardium sands IMPROBABLE Simple Circular geologic formation
Lac du Bonnet, Manitoba ~3.8 75 Sedimentary cover depth PROPOSED Simple Circular magnetic anomaly
Bow City, Alberta 6 <75 Geological dating PROPOSED Complex  No surface expression
Maple Creek, Saskatchewan 6 <75 Geological & radioactive decay dating CONFIRMED Complex Disrupts Late Cretaceous rocks
Purple Springs, Alberta 6 <75 Geological dating PROBABLE Complex  No surface expression
Manson, Iowa ~35 73.8 Ar40-Ar39 melt rock CONFIRMED Central peak No surface evidence
Dumas, Saskatchewan 4 <70 Geological dating PROBABLE Simple Seismic and borehole data
Chicxulub, Yucatan, Mexico 150 66.043 ±0.011 40Ar/39Ar CONFIRMED Peak ring basin Cretaceous-Paleogene

22. 66.043 ±0.011 mA – CRETACEOUS-PALEOGENE EXTINCTION

76% of all species lost — Ammonite 15 cm lengthThe delicate leafy sutures decorating this shell represent some advanced engineering, providing the fortification the squid-like ammonite required to withstand the pressure of deep dives in pursuit of its prey. Dinosaurs may have ruled the land during the Cretaceous period but the oceans belonged to the ammonites. But volcanic activity and climate change already placed the ammonites under stress. The asteroid impact that ended the dinosaurs’ reign provided the final blow. Only a few dwindling species of ammonites survived. Today, the ammonites’ oldest surviving relative is the nautilus. Will it survive the sixth great extinction?

Cretaceous–Paleogene extinction event

CRETACEOUS-TERTIARY/CRETACEOUS-PALEOGENE (K–Pg) BOUNDARY

A major stratigraphic boudary on Earth marking the end of the Mesozoic Era, best known as the age of the dinosaurs. The boundary is defined by a global extinction event that caused the abrupt demise of the majority of all life on Earth. It has been dated to 65 million years ago, coeval with the age of the 200-kilometer-diameter Chicxulub impact structure in Mexico.

Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K–T) boundary – at the Royal Tyrrell Museum Drumheller Alberta.

K/T Boundary: concentrations of the rare platinum group elements (PGEs; Ru, Rh, Pb, Os, Ir, and Pt) and other siderophile elements (e.g., Co, Ni) are enriched by up to 4 orders of magnitude in the thin clay layer marking the K-T boundary compared to those of normal terrestrial crustal rocks. Cretacious/Tertiary boundary (the C abbreviation is already assigned to the Cambrian system), at present practically synonymous with marking the giant mass extinction 65 Ma ago. The extinction of the dinosaurs at that time is only a subordinate part of this remarkable event. See Chicxulub impact structure.

Luis (left) and Walter Alvarez at a limestone outcrop near Gubbio, Italy. Walter’s right hand is touching the top of the Cretaceous limestone, at the K-T boundary. Extraterrestrial Cause of the Cretaceous-Tertiary Extinction a preChicxulub discovery paper-1980 (Image courtesy of Lawrence Berkeley National Laboratory).

The following impacts occurred around the time of the Cretaceous-Paleogene Extinction:The Cretaceous–Paleogene (K–Pg) extinction event, also known as the Cretaceous–Tertiary (K–T) extinction, was a mass extinction of some three-quarters of the plant and animal species on Earth—including all non-avian dinosaurs—that occurred over a geologically short period of time approximately 66 million years ago. With the exception of some ectothermic species in aquatic ecosystems like the leatherback sea turtle and crocodiles, no tetrapods weighing more than 55 pounds (25 kilos) survived. It marked the end of the Cretaceous period and with it, the entire Mesozoic Era, opening the Cenozoic Era that continues today.In the geologic record, the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary, which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows high levels of the metal iridium, which is rare in the Earth’s crust but abundant in asteroids.
Evidence for impact Sedimentary layers found all over the world at the Cretaceous–Paleogene boundary contain a concentration of iridium many times greater than normal. Iridium is extremely rare in Earth’s crust because it is a siderophile element, and therefore most of it traveled with the iron as it sank into Earth’s core during planetary differentiation. Iridium is abundant in most asteroids and comets suggesting that an asteroid struck the Earth at the time of the K–Pg boundary. There were earlier speculations on the possibility of an impact event, but this was the first hard evidence of an impact.In a 2013 paper, Paul Renne of the Berkeley Geochronology Center reported that the date of the asteroid event is 66.043±0.011 million years ago, based on argon–argon dating. He further posits that the mass extinction occurred within 32 thousand years of this date.Renne, Paul R.; (et al) Jan (7 February 2013).

“Time Scales of Critical Events Around the Cretaceous-Paleogene Boundary”. Science 339 (6120)

Extraterrestrial cause for the cretaceoustertiary extinction. (1980 – preChicxulub discovery)

Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Chicxulub, Yucatan, Mexico 150 66.043 ±0.011 40Ar/39Ar CONFIRMED Peak ring basin Cretaceous-Paleogene

23. PALEOCENE: 65.5 – 55.8 MILLION

The dinosaurs and the mammals appeared during the Triassic period, roughly 225 million years ago. The dinosaurs went extinct 65 million years ago. The Mesozoic Era lasted about 180 million years, and is divided into three periods, the Triassic, the Jurassic, and the Cretaceous.
  • Epoch begins with earth devestated by asteroid impact;
  • North America and Eurasia connected off and on;
  • Africa, South America, Antarctica, Australia, and India
    (an island continent) continue to separate;
  • Pacific Ocean shrinks as Atlantic Ocean widens;
  • Climate warm and humid world-wide;
  • Ferns fill post-asteroid world until forests regrow;
  • Mammals, though still small “explode” into the land niches formely dominated by the dinosaurs;
  • Large, flightless birds become top predators;
  • Flowering plants (angiosperms) flourish & spread.
Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Chicxulub, Yucatan, Mexico 150 66.043 ±0.011 40Ar/39Ar CONFIRMED Peak ring basin Cretaceous-Paleogene
Eagle Butte, Alberta 10 <65 Geological dating CONFIRMED Complex Shatter-coned Cretaceous rocks
Parry Peninsula, NWT 160 <65 K/T boundary timeframe IMPROBABLE Complex

24. EOCENE: 55.8 – 33.9 MILLION

By 50 million years ago, dinosaurs were extinct from the Earth. Continental fragments collided, pushing up mountain ranges still existing today. The collision of Africa into Europe gave rise to the Alps in Europe, and the collision of India into Asia formed the Himalaya. Birds and mammals began to expand in number and diversity.
  • Continents continue to separate; Africa & India (an island continent) drift north towards Eurasia;
  • Pacific Ocean shrinks as Atlantic Ocean widens
  • Climate extremely hot & humid; greenhouse conditions allow for tropical forests from pole to pole;
  • Mammals multiply, Primates  proliferate, Whales appear in oceans;
  • Birds are top predators; many modern families appear;
  • Grasses appear but cling to river banks & lake shore;
  • Epoch ends with mass extinction.
Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Montagnais, off Nova Scotia 45 50.5 ± 0.76 K-Ar, 40Ar/39Ar and Rb-Sr CONFIRMED Complex Submerged south of Nova Scotia, Canada
Wanapitei, Ontario 3 to 7.5 37.2 ± 1.2 K/Ar, Ar40-Ar39 melt rock CONFIRMED Simple – Possible flat-floored? Maskelynite – L or LL chondrite projectile
Victoria Island, California 5.5 37-49 Drilling data PROPOSED Simple Geological dating
Mistastin, Labrador 28 36.6 ± 2 Ar40-Ar39 melt rock CONFIRMED Central peak basin Maskelynite
Chesapeake, Virginia ~85 35.5 ± .3 Geological dating CONFIRMED Complex Coesite in suevites

Geochemical Evidence for a Comet Shower in the Late Eocene
K. A. Farley, A. Montanari, E. M. Shoemaker, C. S. Shoemaker

Abstract
Analyses of pelagic limestones indicate that the flux of extraterrestrial helium-3 to Earth was increased for a 2.5-million year (My) period in the late Eocene. The enhancement began ∼1 My before and ended ∼1.5 My after the major impact events that produced the large Popigai and Chesapeake Bay craters ∼36 million years ago. The correlation between increased concentrations of helium-3, a tracer of fine-grained interplanetary dust, and large impacts indicates that the abundance of Earth-crossing objects and dustiness in the inner solar system were simultaneously but only briefly enhanced. These observations provide evidence for a comet shower triggered by an impulsive perturbation of the Oort cloud.


25. 33.9 Ma – EOCENE-OLIGOCENE EXTINCTION

The red dot represents the approximate area of the Mistastin impact 36.4 million years ago in the Paleogene Period.

The 33.9 Ma transition between the end of the Eocene and the beginning of the Oligocene, called the Grande Coupure (the “Great Break” in continuity) in Europe, is marked by large-scale extinction and floral and faunal turnover (although minor in comparison to the largest mass extinctions). Most of the affected organisms were marine or aquatic in nature. They included the last of the ancient cetaceans, the Archaeoceti. This was a time of major climatic change, especially cooling, not obviously linked with any single major impact or any major volcanic event. One cause of the extinction event is speculated to be volcanic activity. Another speculation is that the extinctions are related to several meteorite impacts that occurred about this time. One such event happened near present-day Chesapeake Bay, and another the Popigai crater of central Siberia, scattering debris perhaps as far as Europe. The leading scientific theory on climate cooling at this time is decrease in atmospheric carbon dioxide, which slowly declined in the mid to late Eocene and possibly reached some threshold approximately 34 million years ago. This boundary is closely linked with the Oligocene Oi-1 event, an oxygen isotope excursion that marks the beginning of ice sheet coverage on Antarctica (Wikipedia).

Evidence for Impact: “The late Eocene probably experienced multiple impact events. There are two large impact craters; the 90 km Chesapeake Bay and the 100 km Popigai structures. There are also at least two spherule deposits; the North American (N.A.) microtektites and the slightly older clinopyroxene-bearing (cpx) spherules. Isotopic data are consistent with the N.A. microtektites being derived from the Chesapeake Bay impact and the cpx spherules being derived from the Popigai impact. The late Eocene is also characterized by a 2.5 m.y. anomaly in the flux of 3He that is interpreted to be caused by an increased flux of interplanetary dust, due to a comet shower that may be responsible for all these phenomena.” (Kyte et al, 2002)”Two impacts (Popigai & Chesapeake) — the two biggest in the past 65 million years, and among the biggest of all time — struck Earth with a sudden double punch that might even have been simultaneous. Impacts this size are so rare that the timing was almost certainly no coincidence; perhaps a pair of gravitationally bound asteroids happened to cross Earth’s path. Both impacts seem to have made themselves felt around the world: the Popigai impact was most likely responsible for layers of debris that were dug up in the 1980s in Italy, while the Chesapeake crater is probably responsible for bits of quartz scattered from Georgia to Barbados” (Zimmer, 1998).F. T. Kyte and S. Liu.

IRIDIUM AND SPHERULES IN LATE EOCENE IMPACT DEPOSITS. Lunar and Planetary Science XXXIII (2002)Carl Zimmer.

CRATERS WITHOUT IMPACTDISCOVER Vol. 19 No. 01, January 1998


26. OLIGOCENE: 33.9 – 23 MILLION

  • Continents continue to drift to present positions;
  • Africa and India continue to drift into Eurasia;
  • South America, Antarctica & Australia isolated;
  • Pacific Ocean shrianks as Atlantic Ocean widens;
  • Climate warm but begins to cool;
  • Mammals continue to flourish & grow larger;
  • Apes first appear;
  • Grasses spread; deciduous trees & shrubs spread.

The following impacts “may” be related to the Eocene-Oligocene Extinction:

The red dot represents the approximate area of the Mistastin impact 36.4 million years ago in the Paleogene Period.

The 33.9 Ma transition between the end of the Eocene and the beginning of the Oligocene, called the Grande Coupure (the “Great Break” in continuity) in Europe, is marked by large-scale extinction and floral and faunal turnover (although minor in comparison to the largest mass extinctions). Most of the affected organisms were marine or aquatic in nature. They included the last of the ancient cetaceans, the Archaeoceti. This was a time of major climatic change, especially cooling, not obviously linked with any single major impact or any major volcanic event. One cause of the extinction event is speculated to be volcanic activity. Another speculation is that the extinctions are related to several meteorite impacts that occurred about this time. One such event happened near present-day Chesapeake Bay, and another the Popigai crater of central Siberia, scattering debris perhaps as far as Europe. The leading scientific theory on climate cooling at this time is decrease in atmospheric carbon dioxide, which slowly declined in the mid to late Eocene and possibly reached some threshold approximately 34 million years ago. This boundary is closely linked with the Oligocene Oi-1 event, an oxygen isotope excursion that marks the beginning of ice sheet coverage on Antarctica (Wikipedia).

Evidence for Impact: “The late Eocene probably experienced multiple impact events. There are two large impact craters; the 90 km Chesapeake Bay and the 100 km Popigai structures. There are also at least two spherule deposits; the North American (N.A.) microtektites and the slightly older clinopyroxene-bearing (cpx) spherules. Isotopic data are consistent with the N.A. microtektites being derived from the Chesapeake Bay impact and the cpx spherules being derived from the Popigai impact. The late Eocene is also characterized by a 2.5 m.y. anomaly in the flux of 3He that is interpreted to be caused by an increased flux of interplanetary dust, due to a comet shower that may be responsible for all these phenomena.” (Kyte et al, 2002)”Two impacts (Popigai & Chesapeake) — the two biggest in the past 65 million years, and among the biggest of all time — struck Earth with a sudden double punch that might even have been simultaneous. Impacts this size are so rare that the timing was almost certainly no coincidence; perhaps a pair of gravitationally bound asteroids happened to cross Earth’s path. Both impacts seem to have made themselves felt around the world: the Popigai impact was most likely responsible for layers of debris that were dug up in the 1980s in Italy, while the Chesapeake crater is probably responsible for bits of quartz scattered from Georgia to Barbados” (Zimmer, 1998).F. T. Kyte and S. Liu.

IRIDIUM AND SPHERULES IN LATE EOCENE IMPACT DEPOSITS. Lunar and Planetary Science XXXIII (2002)Carl Zimmer.

CRATERS WITHOUT IMPACTDISCOVER Vol. 19 No. 01, January 1998


27. MIOCENE: 23 – 5.3 MILLION

  • Continents continue to drift to present positions;
  • Africa collides into Eurasia forming the Alps;
  • India collides into Eurasia forming the Himalayas;
  • The Rockies & Andes continue to rise
  • Mediterranean Sea dries up;
  • Global mountain building cools climate; icecaps form;
  • Almost all modern mammal & bird families are present;
  • Grasslands, deciduous trees & shrubs spread;
  • Modern carnivore mammals spread;
  • Hominoid apes flourish and diversify;
  • Isolated South American & Australian marsupials thrive;
  • Kelp forests seals and otters appear in oceans.

28. PLIOCENE: 5.3 – 1.8 MILLION

  • Continents & oceans in current position
  • North & South America connect via Isthmus of Panama, altering global temperatures & currents;
  • Huge Gibraltar waterfall refills Mediterranean Sea;
  • Climate cool, dry and seasonal;
  • All modern plants & animals families present, land & sea;
  • Grasslands, deciduous trees & shrubs spread as tropical forests recede;
  • Land bridges cause migration & mixing of animal species;
  • Carnivores thrive & diversify;
  • First hominids – australopithecinesappear;
  • Many upright, tool-using hominids by end of epoch.

29. PLEISTOCENE: 1.8 MILLION – 10 THOUSAND

The formation of the isthmus connecting North and South America and the split of the Australian continent from Antarctica changed global ocean currents and climate. Ice sheets carved out the Great Lakes of the United States and Canada just 20,000 years ago. Since then, warmer temperatures have melted ice, and sea levels have risen. Map courtesy of CR Scotese, PALEOMAP Project
  • Continents & oceans in current position;
  • Four major glacial advances (ice covered up to 30% of Earth’s surface) followed by interglacial warming;
  • Sea levels drop & rise as glaciers advance and melt;
  • Climate cold & dry world-wide;
  • Epoch ends in mass extinction; esp of megafauna;
  • All modern plant & animal families present, land & sea;
  • Large mammals (megafauna) thrive;
  • Tool-using pre-humans appear in Africa & spread throughout the Old World;
  • Neanderthal humans appear then disappear;
  • Modern humans (Homo sapiens) first appear.

 

Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Pingualuit, Quebec 3.44 1.4 ± 0.1 Ar40-Ar39 melt rock CONFIRMED Simple Overflight of Pingualuit Crater
Barringer, Arizona 1.19 0.049 ± 0.003 Radioactive decay CONFIRMED Simple Jointed
Haviland, Kansas 0.01 0.02  ±0.002 Geological dating CONFIRMED Simple Brenham meteorite

30. ~12,000 years – YOUNGER DRYAS (YD) EXTINCTION

YOUNGER DYRYAS (yd)  Abstracts/Papers

Evidence Of A Global Cataclysm 12,800 Years Ago

These documented crater sites: Bloody Creek Crater, Nova Scotia, Charity Shoal, Ontario, Corossol Crater, Quebec, plus craters in Northern Quebec/Labrador (labeled as “un-detected ice impacts?”): Eclipse Lake, Labrador, and Merewether, Quebec, may reveal impact geology related to the YDB;
Nano Diamonds (n-diamonds, lons-daleite, cubics and other allotropes) are documented (dashed line) at terrestrial sites across North America and Greenland in the Younger Dryas Boundary (YDB) layer dating to 12.9 ka. This corresponds to the Younger Dryas (YD) period when suddenly the planet entered a cooling period lasting 1,300 ± 70 years.

Approximately 13,000 years ago, the earth was emerging from a glacial period, with temperatures approaching modern levels in many areas. In the Younger Dryas (YD) period, suddenly that trend reversed with the planet entering a cooling period lasting 1,300 ± 70 years. During this period the Stone Age Clovis people became extinct along with 35 mammal and 19 bird genera. A thin layer of Black Mat sediment, (YD Boundary – YDB) with a signature of an extraterrestrial impact overlies Clovis-age sites across North America dated ~12.9 ka. Above the YDB containing geology younger than the YD, NO trace of the Clovis people or the extinct 35 mammal and 19 bird genera exist.Black Mat The black organic-rich layer or ‘‘black mat’’ that bridges the Pleistocene-Holocene transition (last deglaciation), is in the form of mollic paleosols, aquolls, diatomites, or algal mats with radiocarbon ages suggesting they are stratigraphic manifestations of the Younger Dryas cooling episode 10,900 B.P. to 9,800 B.P. (radiocarbon years). This layer or mat covers the Clovis-age landscape or surface on which the last remnants of the terminal Pleistocene megafauna are recorded. Stratigraphically and chronologically the extinction appears to have been catastrophic, seemingly too sudden and extensive for either human predation or climate change to have been the primary cause. This sudden Rancholabrean termination at 10,900 ± 50 B.P. appears to have coincided with the sudden climatic switch from Allerød warming to Younger Dryas cooling (Haynes 2008).Evidence for Impact:A characteristic of the YD boundary is varying peak abundances of:(i) magnetic grains with iridium;(ii) magnetic microspherules;(iii) charcoal;(iv) soot;(v) glass-like carbon containing nanodiamonds: In March 2012, researchers identified a nearly 13,000-year-old layer of thin, dark sediment buried in the floor of Lake Cuitzeo in central Mexico. A family of nanodiamonds, including the impact form of nanodiamonds called lonsdaleite*, Lonsdaleite is unique to cosmic impacts and is conclusively identified within this YD layer.*Lonsdaleite (named in honour of Kathleen Lonsdale), also called hexagonal diamond in reference to the crystal structure, is an allotrope of carbon with a hexagonal lattice. In nature, it forms when meteorites containing graphite strike the Earth. The great heat and stress of the impact transforms the graphite into diamond, but retains graphite’s hexagonal crystal lattice. Lonsdaleite was first identified in 1967 from the Canyon Diablo meteorite, where it occurs as microscopic crystals associated with diamond.(vi) carbon spherules: The researchers also found spherules that had collided at high velocities with other spherules during the chaos of impact. Such features could not have formed through anthropogenic, volcanic, or other natural terrestrial processes (Israde-Alcántaraa 2012).

Fast Fourier transform (FFT) is an analytical procedure that produces diffraction patterns for small single crystals. High-resolution transmission electron microscopes (HRTEM) and FFT images of the nanocrystals reveal lattices and d-spacings that are consistent with lonsdaleite. Right is an FFT image of a lonsdaleite crystal from this YD layer. Each spot indicate the reciprocal lattice vector. Image reveals (101) planes with lattice spacing of 1.93 Å, consistent with lonsdaleite (Israde-Alcántaraa 2012).
SEM images of magnetic impact spherules. (A-B) Magnetic impact spherules with dendritic surface pattern. (C) Framboidal pyrite spherule. (D) Collisional magnetic impact spherules. (E) Light microqraph of same magnetic impact spherules. (F) Teardrop-shaped spherule with dendritic pattern. (G) Photomicrograph of same MSps. For labels such as “2.80 #3”, “2.80” represents depth of samples in metres and “#3” is the magnetic impact spherule number (Israde-Alcántaraa 2012).

Based on current data, the following is a preliminary model for formation of the YDB. A comet or asteroid, possibly a previously fragmented object that was once greater than several hundred meters in diameter, entered the atmosphere at a relatively shallow angle (>5° and<30°). Thermal radiation from the air shock reaching Earth’s surface was intense enough to pyrolyze biomass and melt silicate minerals below the flight path of the impactor. Pyrolytic products were oxidized, locally depleting the atmosphere of oxygen, and within microseconds, residual free carbon condensed into diamond-like crystal structures, carbon spherules, carbon onions, and aciniform soot. This involved a carbon vapor deposition like process similar to diamond-formation during TNT detonation. In some cases, carbon onions grew around the nanodiamonds and other nanomaterials. At the same time, iron-rich and silicate materials may have melted to form magnetic spherules. Several seconds later, depending on the height of the thermal radiation source, the air shock arrived. Nanodiamonds, magnetic spherules, carbon spherules, and other markers were lofted by the shock-heated air into the upper atmosphere, where prevailing winds distributed them across the Northern and Southern Hemispheres. We suggest that the above model can account for the observed YDB markers (Israde-Alcántaraa et al, 2012).

Map showing 24 sites containing Younger Dryas Boundary (YDB) nanodiamonds. The solid line defines the current known limits of the YDB field of cosmic-impact proxies, spanning 50 million km2 (Wittke et al. 2013), including the study of Mahaney et al. (2010) in Venezuela (open circle). Numbered sites are from this study: (1) Lake Cuitzeo, Mexico (Israde-Alca´ntara et al. 2012b); (2) Daisy Cave, California; (3) Arlington Canyon, California (Kennett et al. 2009b); (4) Murray Springs, Arizona (Kennett et al. 2009a); (5) Lindenmeier, Colorado; (6) Bull Creek, Oklahoma (Kennett et al. 2009a); (7) Blackville, South Carolina; (8) Topper, South Carolina (Kennett et al. 2009a); (9) Kimbel Bay, North Carolina; (10) Newtonville, New Jersey; (11) Melrose, Pennsylvania; (12) Sheriden Cave, Ohio; (13) Gainey, Michigan (Kennett et al. 2009a); (14) Chobot site, Alberta, Canada (Kennett et al. 2009a); (15) Lake Hind, Manitoba, Canada (Kennett et al. 2009a); (16) Kangerlussuaq, Greenland (Kurbatov et al. 2010); (17) Watcombe Bottom, Isle of Wight, United Kingdom; (18) Lommel, Belgium; (19) Ommen, Belgium; (20) Lingen, Germany; (21) Santa Maira, Spain; (22) Abu Hureyra, Syria. In addition, independent researchers have reported NDs at six sites, indicated by letters, four of which are in common: (a) Indian Creek, Montana (Baker et al. 2008); (b) Bull Creek, Oklahoma (Madden et al. 2012; Bement et al. 2014); (c) Sheriden Cave, Ohio (Redmond and Tankersley 2011); (d) Newtonville, New Jersey (Demitroff et al. 2009); (e) Lommel, Belgium (Tian et al. 2011); (f) Aalsterhut, Netherlands (van Hoesel et al. 2012). (Kinzie et al, 2014).

References

Grieve R.A.F., Robertson P.B., IMPACT STRUCTURES IN CANADA, the Journal of the Royal Astronomical Society of Canada, February 1975

Kraus et al, Nanosecond formation of diamond and lonsdaleite by shock compression of graphite, Nature Communications 7, Article number: 10970 14 March 2016

Meen V.B., MEREWETHER CRATER – A POSSIBLE METEORITE CRATER,the Proceedings of the Geological Association Canada 1957 pp 49-67. (unless otherwise noted, the Merewether data quoted above is from this paper).

Ian SPOONER, George STEVENS, Jared MORROW, Peir PUFAHL, Richard GRIEVE, Rob RAESIDE, Jean PILON, Cliff STANLEY, Sandra BARR, and David MCMULLIN, Identification of the Bloody Creek structure, a possible impact crater in southwestern Nova Scotia, Canada.Meteoritics & Planetary Science 44, Nr 8, 1193–1202 (2009)

Haynes, C. V., Younger Dryas ‘‘black mats’’ and the Rancholabrean termination in North AmericaDepartments of Anthropology and Geosciences, Arizona, January 23, 2008.

Isabel Israde-Alcántara, James L. Bischoff, Gabriela Domínguez-Vázquez, Hong-Chun Li, Paul S. DeCarli, Ted E. Bunch, James H. Wittke, James C. Weaver, Richard B. Firestone, Allen West, James P. Kennett, Chris Mercer, Sujing Xie, Eric K. Richman, Charles R. Kinzie, and Wendy S. Wolbach, Evidence from central Mexico supporting the Younger Dryas extraterrestrial impact hypothesis, University of Hawaii, Honolulu, HI, January 31, 2012

Kinzie et al, 2014 Nanodiamond-Rich Layer across Three Continents Consistent with Major Cosmic Impact at 12,800 Cal BP.The Journal of Geology, 2014, volume 122.

Nicholas Pintera, Andrew C. Scottb, Tyrone L. Daultonc, Andrew Podolla, Christian Koeberld, R. Scott Andersone, Scott E. Ishmana, The Younger Dryas impact hypothesis: A requiem, Earth-Science Reviews, Volume 106, June 2011

Zamora, A. Solving the Mystery of the Carolina Bays

Younger Dryas Extinction Impact Related? (Bloody Creek @ 29:30).

My Younger Dryas blog presentation in the Den of Lor.
Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Carolina Bays, NC Various ~0.0129-0.14 Not firmly quantified PROPOSED Simple Younger Drias black mat
Bloody Creek, Nova Scotia 0.350 X 0.420 ~0.012 Geological dating PROBABLE Simple  Elliptical basin
Corossol Structure, Gulf of St. Lawrence 4.0 ~0.012 14C age shells in sediments PROPOSED Complex Underwater Gulf St. Lawrence
Jocko, Ontario >0.2 <0.012 Created in glacial remains IMPROBABLE Simple Ground Exploration Video
Plevna/Tomvale Structure, ONTARIO ~0.01 <0.012 Created in glacial remains IMPROBABLE Simple
Whitecourt, Alberta 0.036 0.00113 14C dating of charcoal CONFIRMED Simple Medium octahedrite (Om) IIIAB
Charity Shoal, Lake Ontario ~1  ? PROPOSED Simple underwater Lake Ontario Negative magnetic anomaly

31. HOLOCENE: 10 THOUSAND – PRESENT

  • Continents & oceans in current position; sea levels rise;
  • Climate warming partly due to human industrialism;
  • Mass extinction in progress due to human proliferation;
  • Human civilization dominates most Earth ecosystems;
  • Epoch opens with many Pleistocene animals extinct;
  • Few new plants or animals appear;
  • Human selction supercedes natural selction – humans favor beneficial plants and animals; neglect others;
  • Human culture significantly alters natural landscape;
  • Human genetic technology manipulates Earth’s life at the most fundamental level.

 


32. 50 MILLION YEARS IN THE FUTURE


33. GEOLOGIC AGE vs IMPACT

Crater list of known impact craters documented by R. A. F. Grieve and P. B. Robertson – 1979.
Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Viewfield, Saskatchewan 2.5 190 ± 20 Geological dating CONFIRMED Simple Jurassic-Triasic post-impact deposit
Cloud Creek, Wyoming 7 ~190 ± 30 Geological dating CONFIRMED Complex Chronostratigraphic
Hartney, Manitoba 6 <190 ± 20 Geological dating PROBABLE Complex? Structurally uplifted centre
Upheaval Dome, Utah 5.5 <170 Geological dating CONFIRMED Complex Younger than the Jurassic Navajo Sandstone
Miami Florida Crater/Structure ~1 ~140 After Florida Plateau deposition IMPROBABLE Complex? Underwater off Miami
CRATER DIA (km) AGE (Ma)
Chicxulub, Yucatan, Mexico 150 66.043 ±0.011
Eagle Butte, Alberta 10 <65
Manson, Iowa ~35 73.8
Maple Creek, Saskatchewan 6 <75
CRATER DIA (km) AGE (Ma)
Popigai, Russia 90 35.7 ± 0.2
Chesapeake, Virginia 40 35.5 ± 4
Mistastin 28 36.4 ± 4
Wanapitei 3 to 7.5 37.2 ± 1.2
CRATER DIA (km) AGE (Ma)
Popigai, Russia 90 35.7 ± 0.2
Chesapeake, Virginia 40 35.5 ± 4
Mistastin 28 36.4 ± 4
Wanapitei 3 to 7.5 37.2 ± 1.2

The following impacts “may” be related to the Younger Dryas Extinction:

CRATER DIA (km) AGE (Ma) NOTES
Merewether, Labrador 0.19812 (largest of three) ? Un-detected ice impact
Bloody Creek, Nova Scotia 0.350 X 0.420 ~12,000 years? Video Documentary @ 29:30
Charity Shoal, Lake Ontario ~1 ?
Eclipse Lake, Labrador 1.5 ? Un-detected ice impact
Corossol Crater, Quebec 4 ?

Included are craters in Northern Quebec/Labrador (labeled as “un-detected ice impacts?”).

PERIOD NAME/PLACE Age (million years) Date Related Extinction Notes
Orosirian Vredefort, South Africa 1,970
Orosirian Sudbury, Ontario, Canada 1,850 Sudbury Distal Ejecta
Cryogenian Janisjarvi, Russia 700
Ediacaran Beaverhead, Idaho, USA ~600
Ediacaran Kelly West, N.T., Australia 550
Ediacaran Holleford, Ontario, Canada 550 Overflight of Holleford Crater
Cambrian Kjardla, Estonia 500
Cambrian Presqu’ile , Quebec, Canada <500 Geological dating
Cambrian Saaksjarvi, Finland 490
Ordovician Carswell, Saskatchewan, Canada 485
Ordovician Clearwater East, Quebec, Canada ~460–470
Ordovician Pilot Lake, N.W.T. Canada 445 Ordovician
Silurian Slate Islands, Ontario, Canada 436 Ordovician
Silurian Rock Elm, Saskatchewan, Canada 420-440 Ordovician
Silurian Lac Couture, Quebec, Canada 425
Devonian Lac La Moinerie, Quebec, Canada 400 Late Devonian
Devonian Brent, Ontario, Canada 396 Late Devonian Overflight of Brent Crater
Devonian Elbow, Saskatchewan, Canada 395 Late Devonian Geological dating
Devonian Siljan, Sweden 365
Devonian Flynn Creek, Tennessee, USA 360
Carboniferous Charlevoix, Quebec, Canada 342 Late Devonian Elevated Earthquake Zone
Carboniferous Crooked Creek, Missouri, USA 320
Carboniferous Middlesboro, Kentucky, USA 300
Carboniferous Serpent Mound, Ohio, USA 300
Carboniferous Ile Rouleau, Quebec, Canada <300 Geological dating
Permian Clearwater West, Quebec, Canada 290
Triassic Gow, Saskatchewan, Canada <250 Permian–Triassic (P–Tr) extinction event
Triassic Kursk, Russia 250
Triassic Dellen, Sweden 230
Triassic St. Martin, Manitoba, Canada 219 Late Triassic
Triassic Manicouagan, Quebec, Canada 214 end-middle Norian
Jurassic Red Wing, North Dakota, USA 200 Late Triassic/Triassic-Jurassic
Jurassic Viewfield, Saskatchewan, Canada 190 Triassic-Jurassic
Jurassic Upheaval Dome, Utah, USA <170 Geological dating
Jurassic Vepriaj, Lithuania 160
Jurassic Rochechouart, France 160
Jurassic Strangways, N.T., Australia 150
Cretaceous Carswell, Saskatchewan, Canada 115
Cretaceous Sierra Madre, Texas, USA 100
Cretaceous West Hawk, Ontario, Canada 100 Geological dating
Cretaceous Deep Bay, Saskatchewan, Canada 99 Geological dating
Cretaceous Maple Creek, Saskatchewan, Canada <75 Geological dating
Cretaceous Rotmistrovka, Ukraine 70
Cretaceous Chicxulub, Yucatan, Mexico 66.043 ±0.011 CRETACEOUS-PALEOGENE
Paleogene Eagle Butte, Alberta, Canada <65 Geological dating
Paleogene Kara, Russia 57
Paleogene Montagnais, Nova Scotia, Canada 50
Paleogene Mistastin, Labrador, Canada 36
Paleogene Wanapitei, Ontario, Canada 37
Neogene Haughton Dome, N.W.T., Canada 15
Neogene Karla, Russia 10
Neogene Aouelloul, Mauritania 3.1
Quaternary Pingualuit, Quebec, Canada 1.4 Overflight of Pingualuit Crater
Quaternary Bosumtwi, Ghana 1.3
Quaternary Lonar, India 0.05
Quaternary Barringer, Arizona, USA 0.049 Jointed
Quaternary Whitecourt Alberta, Canada 0.00113

34. REFERENCE

The period dichotomy in terrestrial impact crater ages

Richard B. Stothers

Abstract

Impact cratering on the Earth during the past 250 Myr has occurred with either of two apparent periodicities, ∼30 or ∼35 Myr, depending on the set of impact crater ages that is adopted. When the craters are segregated by size and the possible age errors are explicitly taken into account in the analysis, only the longer periodicity survives, and does so only in the case of the largest craters (diameters ≥ 35 km). Smaller craters exhibit no robust periodicity. Despite their relative abundance, the inclusion of data points for the small craters merely degrades, without shifting or destroying, the periodic signal of the largest craters when all of the craters are analysed together. The possible consequences for quasi-periodic Galactic perturbations of the Oort comet cloud are briefly discussed. (Monthly Notices of the Royal Astronomical Society 01 January 2006)

Impact cratering and the Oort Cloud

J. T. Wickramasinghe & W. M. Napier

Abstract

We calculate the expected flux profile of comets into the planetary system from the Oort Cloud arising from Galactic tides and encounters with molecular clouds. We find that both periodic and sporadic bombardment episodes, with amplitudes an order of magnitude above background, occur on characteristic time-scales ∼25–35 Myr. Bombardment episodes occurring preferentially during spiral arm crossings may be responsible both for mass extinctions of life and the transfer of viable microorganisms from the bombarded Earth into the disturbing nebulae. Good agreement is found between the theoretical expectations and the age distribution of large, well-dated terrestrial impact craters of the past 250 Myr. A weak periodicity of ∼36 Myr in the cratering record is consistent with the Sun’s recent passage through the Galactic plane, and implies a central plane density ∼0.15 M pc−3. This leaves little room for a significant dark matter component in the disc. (Monthly Notices of the Royal Astronomical Society 07 May 2008)

Disc dark matter in the Galaxy and potential cycles of extraterrestrial impacts, mass extinctions and geological events

Michael R. Rampino

Abstract

A cycle in the range of 26–30 Myr has been reported in mass extinctions, and terrestrial impact cratering may exhibit a similar cycle of 31 ± 5 Myr. These cycles have been attributed to the Sun’s vertical oscillations through the Galactic disc, estimated to take from ∼30 to 42 Myr between Galactic plane crossings. Near the Galactic mid-plane, the Solar system’s Oort Cloud comets could be perturbed by Galactic tidal forces, and possibly a thin dark matter (DM) disc, which might produce periodic comet showers and extinctions on the Earth. Passage of the Earth through especially dense clumps of DM, composed of Weakly Interacting Massive Particles (WIMPs) in the Galactic plane, could also lead to heating in the core of the planet through capture and subsequent annihilation of DM particles. This new source of periodic heating in the Earth’s interior might explain a similar ∼30 Myr periodicity observed in terrestrial geologic activity, which may also be involved in extinctions. These results suggest that cycles of geological and biological evolution on the Earth may be partly controlled by the rhythms of Galactic dynamics. (Monthly Notices of the Royal Astronomical Society 18 February 2015)

Periodic impact cratering and extinction events over the last 260 million years

Michael R. Rampino  & Ken Caldeira

Abstract

The claims of periodicity in impact cratering and biological extinction events are controversial. A newly revised record of dated impact craters has been analyzed for periodicity, and compared with the record of extinctions over the past 260 Myr. A digital circular spectral analysis of 37 crater ages (ranging in age from 15 to 254 Myr ago) yielded evidence for a significant 25.8 ± 0.6 Myr cycle. Using the same method, we found a significant 27.0 ± 0.7 Myr cycle in the dates of the eight recognized marine extinction events over the same period. The cycles detected in impacts and extinctions have a similar phase. The impact crater dataset shows 11 apparent peaks in the last 260 Myr, at least 5 of which correlate closely with significant extinction peaks. These results suggest that the hypothesis of periodic impacts and extinction events is still viable. (Monthly Notices of the Royal Astronomical Society 20 October 2015)

A tale of clusters: no resolvable periodicity in the terrestrial impact cratering record

Matthias M. M. Meier & Sanna Holm-Alwmark

Abstract

Rampino & Caldeira carry out a circular spectral analysis (CSA) of the terrestrial impact cratering record over the past 260 million years (Ma), and suggest a ∼26 Ma periodicity of impact events. For some of the impacts in that analysis, new accurate and high-precision (‘robust’; 2SE < 2 per cent) 40Ar-39Ar ages have recently been published, resulting in significant age shifts. In a CSA of the updated impact age list, the periodicity is strongly reduced. In a CSA of a list containing only impacts with robust ages, we find no significant periodicity for the last 500 Ma. We show that if we relax the assumption of a fully periodic impact record, assuming it to be a mix of a periodic and a random component instead, we should have found a periodic component if it contributes more than ∼80 per cent of the impacts in the last 260 Ma. The difference between our CSA and the one by Rampino & Caldeira originates in a subset of ‘clustered’ impacts (i.e. with overlapping ages). The ∼26 Ma periodicity seemingly carried by these clusters alone is strongly significant if tested against a random distribution of ages, but this significance disappears if it is tested against a distribution containing (randomly spaced) clusters. The presence of a few impact age clusters (e.g. from asteroid break-up events) in an otherwise random impact record can thus give rise to false periodicity peaks in a CSA. There is currently no evidence for periodicity in the impact record. (Monthly Notices of the Royal Astronomical Society 25 January 2017)