EXTINCTIONS vs POSSIBLE IMPACT

EXTINCTIONS VS Possible Impact Relationship

by: Charles O’Dale

Also see: Crater Impact Age vs Epoch

  • 1. INTRODUCTION
  • 2. EXTINCTIONS:
    • ~12,000 years – YOUNGER DRYAS (YD) EXTINCTION;
    • 33.9 Ma – EOCENE-OLIGOCENE EXTINCTION;
    • 66.043 ±0.011 mA – CRETACEOUS-PALEOGENE EXTINCTION;
    • 201.3 Ma – TRIASSIC-JURASSIC EXTINCTION;
    • ~214 Ma – LATE TRIASSIC EXTINCTION (extinction at the Carnian/Norian boundary – 227 Ma);
    • 252.28 Ma – PERMIAN-TRIASSIC EXTINCTION;
    • ~374 Ma – LATE DEVONIAN EXTINCTION; and
    • ~450 Ma – ORDOVICIAN EXTINCTION.
  • 3. GEOLOGICAL PERIODS VS IMPACTS
  • 4. REFERENCE PAPERS

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.

Extinction Event

2. EXTINCTIONS

~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).

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?”).

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 America Departments 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.

33.9 Ma – EOCENE-OLIGOCENE EXTINCTION

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.
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 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 IMPACT DISCOVER Vol. 19 No. 01, January 1998


66.043 ±0.011 mA – CRETACEOUS-PALEOGENE EXTINCTION

76% of all species lost — Ammonite 15 cm length

The 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:

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

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)


201.3 Ma – TRIASSIC-JURASSIC EXTINCTION

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

CRATER DIA (km) AGE (Ma)
Red Wing 9.1 200 ± 25
Viewfield 2.5 190 ± 20
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


~214 Ma – LATE TRIASSIC EXTINCTION

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.
The following impacts “may” be related to the Late Triassic Extinction:

CRATER DIA (km) AGE (Ma)
Red Wing, Minnesota 9.1 200 ± 25
Saint Martin, Manitoba ~40 219 ± 40
Manicouagan, Quebec 100 214 ± 1
Rochechouart, Europe 23 186 ± 5
Obolon, Ukraine 20 169 ± 7
Paasselka, Finland 10 228.7 ± 3.4

 

 

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


252.28 Ma – PERMIAN-TRIASSIC 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 following impact “may” be related to the Permian–Triassic (P–Tr) extinction event:

CRATER DIA (km) AGE (Ma)
Gow 5 <250

 

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).


~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 following impacts “may” be related to the Late Devonian Extinction:

CRATER DIA (km) AGE (Ma)
Siljan, Sweden 52 368 ± 1
Charlevoix 46 360 ± 25
Kaluga, Russia 15 380 ± 10
Panther Mountain, New York 10 ~375
Lac La Moinerie, Quebec 8 400 ± 50
Elbow, Saskatchewan 8 395 ± 25
Crooked Creek, Missouri 5.6 360 ± 80
Brent, Ontario 3.8 396 ± 20
Flynn Creek, Tennessee 3.8 360 ± 20

 

THE LATE DEVONIAN MASS EXTINCTION EVENT

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.


~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.

Researchers have discovered minerals from 43 meteorites that landed on Earth 470 million years ago. More than half of the mineral grains are from meteorites completely unknown or very rare in today’s meteorite flow. These findings mean that we will probably need to revise our current understanding of the history and development of the solar system. 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 following impacts “may” be related to the Ordovician Extinction:

CRATER DIA (km) AGE (Ma) NOTES
Slate Islands, Ontario 32 436 ± 3 Multiple impact?
Clearwater East, Quebec 26 ~460–470 Possible Multiple Impact?
Ames, OK 15 470 ± 30 Multiple impact?
Lac Couture, Quebec 8 425 ± 25
Calvin, Michigan 7.24 450 ± 10
Decorah, Iowa 6 360 ± 25 Multiple impact?
Rock Elm, Wisconsin 6 420 – 440 Multiple impact?
Pilot Lake, NWT 6 445 ± 2
Brent, Ontario 3.8 396 ± 20 Overflight of Brent Crater

 

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.


3. GEOLOGICAL PERIODS VS IMPACTS

Crater list of known impact craters documented by R. A. F. Grieve and P. B. Robertson – 1979.

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

 

Comparison of commonly used dating methods.

Name of Method Age range of Application Material Dated Methodology
Radiocarbon 1 – 70,000 years Organic material such as bones, wood, charcoal, shells Radioactive decay of 14C in organic matter after removal from bioshpere
K-Ar dating 1,000 – billion of years Potassium-bearing minerals and glasses Radioactive decay of 40K in rocks and minerals
Uranium-Lead 10,000 – billion of years Uranium-bearing minerals Radioactive decay of uranium to lead via two separate decay chains
Uranium series 1,000 – 500,000 years Uranium-bearing minerals, corals, shells, teeth, CaCO3 Radioactive decay of 234U to 230Th
Fission track 1,000 – billion of years Uranium-bearing minerals and glasses Measurement of damage tracks in glass and minerals from the radioactive decay of 238U
Luminescence (optically or thermally stimulated) 1,000 – 1,000,000 years Quartz, feldspar, stone tools, pottery Burial or heating age based on the accumulation of radiation-induced damage to electron sitting in mineral lattices
Cosmogenic Nuclides 1,000 – 5,000,000 years Typically quartz or olivine from volcanic or sedimentary rocks Radioactive decay of cosmic-ray generated nuclides in surficial environments
Magnetostratigraphy 20,000 – billion of years Sedimentary and volcanic rocks Measurement of ancient polarity of the earth’s magnetic field recorded in a stratigraphic succession
Tephrochronology 100 – billions of years Volcanic ejecta Uses chemistry and age of volcanic deposits to establish links between distant stratigraphic successions

4. REFERENCE PAPERS

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)