EXTINCTIONS VS Possible Impact Relationship
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
~12,000 years – YOUNGER DRYAS (YD) EXTINCTION
The following impacts “may” be related to the Younger Dryas Extinction:
Included may be craters in Northern Quebec/Labrador (labeled as “un-detected ice impacts?”).
|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;
(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).
|YD Impact Model
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).
ABSTRACT A major cosmic-impact event has been proposed at the onset of the Younger Dryas (YD) cooling episode at ≈12,800 ±150 years before present, forming the YD Boundary (YDB) layer, distributed over 150 million km2 on four continents. In 24 dated stratigraphic sections in 10 countries of the Northern Hemisphere, the YDB layer contains a clearly defined abundance peak in nanodiamonds (NDs), a major cosmic-impact proxy. Observed ND polytypes include cubic diamonds, lonsdaleite-like crystals, and diamond-like carbon nanoparticles, called n-diamond and i-carbon. The ND abundances in bulk YDB sediments ranged up to ≈500 ppb (mean: 200 ppb) and that in carbon spherules up to ≈3700 ppb (mean: ≈750 ppb); 138 of 205 sediment samples (67%) contained no detectable NDs. Isotopic evidence indicates that YDB NDs were produced from terrestrial carbon, as with other impact diamonds, and were not derived from the impactor itself. The YDB layer is also marked by abundance peaks in other impact-related proxies, including cosmic-impact spherules, carbon spherules (some containing NDs), iridium, osmium, platinum, charcoal, aciniform carbon (soot), and high-temperature melt-glass. This contribution reviews the debate about the presence, abundance, and origin of the concentration peak in YDB NDs. We describe an updated protocol for the extraction and concentration of NDs from sediment, carbon spherules, and ice, and we describe the basis for identification and classification of YDB ND polytypes, using nine analytical approaches. The large body of evidence now obtained about YDB NDs is strongly consistent with an origin by cosmic impact at ≈12,800 cal BP and is inconsistent with formation of YDB NDs by natural terrestrial processes, including wildfires, anthropogenesis, and/or influx of cosmic dust. (Kinzie et al, 2014)
|Nanosecond formation of diamond and lonsdaleite by shock compression of graphite
The shock-induced transition from graphite to diamond has been of great scientific and technological interest since the discovery of microscopic diamonds in remnants of explosively driven graphite. Furthermore, shock synthesis of diamond and lonsdaleite, a speculative hexagonal carbon polymorph with unique hardness, is expected to happen during violent meteor impacts. Here, we show unprecedented in situ X-ray diffraction measurements of diamond formation on nanosecond timescales by shock compression of pyrolytic as well as polycrystalline graphite to pressures from 19 GPa up to 228 GPa. While we observe the transition to diamond starting at 50 GPa for both pyrolytic and polycrystalline graphite, we also record the direct formation of lonsdaleite above 170 GPa for pyrolytic samples only. Our experiment provides new insights into the processes of the shock-induced transition from graphite to diamond and uniquely resolves the dynamics that explain the main natural occurrence of the lonsdaleite crystal structure being close to meteor impact sites. (Kraus et al 2016)
|Solving the Mystery of the Carolina Bays – Video Documentary
The origin of the Carolina Bays presents a formidable puzzle for geologists and astronomers. The elliptical bays with sandy rims look like they were made by huge impacts, but they do not have the characteristic markers associated with extraterrestrial impacts. The dates of the terrain on which the bays are found span millennia, forcing scientists to conclude that the bays must have been made by the action of wind and water over the last 140,000 years. A new geometrical survey has found that the Carolina Bays are perfect ellipses with similar width-to-length ratios as the Nebraska rainwater basins. This book starts from the premise that if the Carolina Bays are conic sections, they must have originated from oblique conical cavities that were transformed by geological processes to their current form. Mathematical analysis following this line of reasoning provides clues supporting the idea that the Earth was hit during the ice age by an extraterrestrial object. The impact may have triggered the Younger Dryas cold event and caused the extinction of the North American megafauna and the Clovis culture. The Carolina Bays are the remodeled remains of oblique conical craters formed on ground liquefied by secondary impacts of glacier ice boulders ejected from the primary impact site.(Zamora 2016)
The Younger Dryas impact hypothesis: A requiem
The Younger Dryas (YD) impact hypothesis is a recent theory that suggests that a cometary or meteoritic body or bodies hit and/or exploded over North America 12,900 years ago, causing the YD climate episode, extinction of Pleistocene megafauna, demise of the Clovis archeological culture, and a range of other effects. Since gaining widespread attention in 2007, substantial research has focused on testing the 12 main signatures presented as evidence of a catastrophic extraterrestrial event 12,900 years ago. Here we present a review of the impact hypothesis, including its evolution and current variants, and of efforts to test and corroborate the hypothesis.
The physical evidence interpreted as signatures of an impact event can be separated into two groups. The first group consists of evidence that has been largely rejected by the scientific community and is no longer in widespread discussion, including: particle tracks in archeological chert; magnetic nodules in Pleistocene bones; impact origin of the Carolina Bays; and elevated concentrations of radioactivity, iridium, and fullerenes enriched in 3He. The second group consists of evidence that has been active in recent research and discussions: carbon spheres and elongates, magnetic grains and magnetic spherules, byproducts of catastrophic wildfire, and nanodiamonds. Over time, however, these signatures have also seen contrary evidence rather than support. Recent studies have shown that carbon spheres and elongates do not represent extraterrestrial carbon nor impact-induced megafires, but are indistinguishable from fungal sclerotia and arthropod fecal material that are a small but common component of many terrestrial deposits. Magnetic grains and spherules are heterogeneously distributed in sediments, but reported measurements of unique peaks in concentrations at the YD onset have yet to be reproduced. The magnetic grains are certainly just iron-rich detrital grains, whereas reported YD magnetic spherules are consistent with the diffuse, non-catastrophic input of micrometeorite ablation fallout, probably augmented by anthropogenic and other terrestrial spherular grains. Results here also show considerable subjectivity in the reported sampling methods that may explain the purported YD spherule concentration peaks. Fire is a pervasive earth-surface process, and reanalyses of the original YD sites and of coeval records show episodic fire on the landscape through the latest Pleistocene, with no unique fire event at the onset of the YD. Lastly, with YD impact proponents increasingly retreating to nanodiamonds (cubic, hexagonal [lonsdaleite], and the proposed n-diamond) as evidence of impact, those data have been called into question. The presence of lonsdaleite was reported as proof of impact-related shock processes, but the evidence presented was inconsistent with lonsdaleite and consistent instead with polycrystalline aggregates of graphene and graphane mixtures that are ubiquitous in carbon forms isolated from sediments ranging from modern to pre-YD age. Important questions remain regarding the origins and distribution of other diamond forms (e.g., cubic nanodiamonds).
In summary, none of the original YD impact signatures have been subsequently corroborated by independent tests. Of the 12 original lines of evidence, seven have so far proven to be non-reproducible. The remaining signatures instead seem to represent either (1) non-catastrophic mechanisms, and/or (2) terrestrial rather than extraterrestrial or impact-related sources. In all of these cases, sparse but ubiquitous materials seem to have been misreported and misinterpreted as singular peaks at the onset of the YD. Throughout the arc of this hypothesis, recognized and expected impact markers were not found, leading to proposed YD impactors and impact processes that were novel, self-contradictory, rapidly changing, and sometimes defying the laws of physics. The YD impact hypothesis provides a cautionary tale for researchers, the scientific community, the press, and the broader public. (Pinter et al 2011)
Comprehensive analysis of nanodiamond evidence relating to the Younger Dryas Impact Hypothesis
19 December 2016
Tyrone L. Daulton, Sachiko Amari, Andrew C. Scott, Mark Hardiman, Nicholas Pinter, R. Scott Anderson
During the end of the last glacial period in the Northern Hemisphere near 12.9k cal a BP, deglacial warming of the Bølling–Ållerod interstadial ceased abruptly and the climate returned to glacial conditions for an interval of about 1300 years known as the Younger Dryas stadial. The Younger Dryas Impact Hypothesis proposes that the onset of the Younger Dryas climate reversal, Pleistocene megafaunal extinctions and disappearance of the Clovis paleoindian lithic technology were coeval and caused by continent-wide catastrophic effects of impact/bolide events in North America. While there are no known impact structures dated to the Younger Dryas onset, physical evidence of the impact/bolide events is argued to be present in sediments spanning several continents at stratigraphic levels inferred to date to the Bølling-Ållerod/Younger Dryas boundary (YDB). Reports of nanometer to submicron-sized diamonds in YDB sediments, in particular the rare 2H hexagonal polytype of diamond, lonsdaleite, have been presented as strong evidence for shock processing of crustal materials. We review the available data on diamonds in sediments and provide new data. We find no evidence for lonsdaleite in YDB sediments and find no evidence of a spike in nanodiamond concentration at the YDB layer to support the impact hypothesis.
Palaeolithic extinctions and the Taurid Complex
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).
33.9 Ma – EOCENE-OLIGOCENE EXTINCTION
The following impacts “may” be related to the Eocene-Oligocene Extinction:
|CRATER||DIA (km)||AGE (Ma)||NOTES|
|Popigai, Russia||90||35.7 ± 0.2||Double impact?|
|Chesapeake, Virginia||40||35.5 ± 4||Double impact?|
|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
The following impacts occurred around the time of the Cretaceous-Paleogene Extinction:
|CRATER||DIA (km)||AGE (Ma)||NOTES|
|Chicxulub, Yucatan, Mexico||150||66.043 ±0.011|
|Eagle Butte, Alberta||10||<65|
|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)
201.3 Ma – TRIASSIC-JURASSIC EXTINCTION
The following impacts “may” be related to the Triassic–Jurassic Extinction:
|CRATER||DIA (km)||AGE (Ma)||NOTES|
|Red Wing||9.1||200 ± 25|
|Viewfield||2.5||190 ± 20|
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
The following impacts “may” be related to the Late Triassic Extinction:
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).
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).
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.
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
252.28 Ma – PERMIAN-TRIASSIC EXTINCTION
The following impact “may” be related to 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).
~374 Ma – LATE DEVONIAN EXTINCTION
The following impacts “may” be related to the Late Devonian Extinction:
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.
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
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 following impacts “may” be related to the Ordovician Extinction:
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. 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.
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.