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Mass Extinctions and Meteorite Impacts

The views expressed are those of the author and are not necessarily those of Scientific American.


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The flyby of asteroid 2012 DA14 and especially the past and present Russian meteors are impressive reminders that the terrestrial biosphere can be affected also by extraterrestrial forces. However contrary to headlines by the general media the connection between mass extinctions and large meteor impacts is still poorly understand.

The Scaglia Variegata and Scaglia Cinerea are two geological formations deposited during the late Eocene and early Oligocene (36 and respectively 33 million years ago). This period of transition is characterized by profound climatic changes and a biological crisis at a global scale. In less than a million years about 20% of genera of marine organisms became extinct. The causes of this mass extinction are not yet entirely clear. The gradual hypothesis invokes the slow drift of continents (especially the drift of Antarctica to the South Pole and subsequent global cooling effect) and the resulting climatic and environmental changes; the catastrophic hypothesis invokes the impact of a meteorite as the main cause of the sudden biological crisis.

In fact two very large impact craters are dated into the Eocene: Chesapeake Bay (located in North- America) and Popigai (Siberia). Popigai Crater is with a diameter of 100 km one of the largest impact craters on our planet (and the largest formed in the last 65 million years), followed by the 85 km large Chesapeake Bay Crater.

Some clues to solve the mystery about the biological crisis at the end of the Eocene are found in the sediments exposed in the quarry of Massignano, named after a small village near the Italian city of Ancona.

Fig.1. The Eocene-Oligocene transition in the quarry of Massignano (Marche – Italy), above sediment bed 17 (top of the quarry).

At the base of the outcrop with the Scaglia Variegata and Scaglia Cinerea formations two thin layers have been identified, characterized by abnormal concentrations of the element Iridium and the isotope Helium-3. Both substances are depleted in the rocks of earth’s crust, but quite concentrated in extraterrestrial material. These layers also contain spherules of the minerals spinel and quartz, displaying a lamellar and shattered structure. Such grains can be formed only by high temperatures and high pressure as experienced during an impact.

It seems almost certain that two objects of  extraterrestrial origin hit earth during the transition from the Eocene to the Oligocene, but it appears also that the effects of both impacts on terrestrial ecosystems were very limited. Complicating the question how large impacts affect the life on earth are also temporal uncertainties. According to some dating results the two mentioned impacts do not coincide with the Eocene extinction phase (between 37 to 38 million years ago) or the Eocene-Oligocene boundary (35,5 to 36,0 million years ago), but occurred 1 to 2 million years before and respectively after these periods.

Fig.2. “Raup´s Kill Curve”, named after paleontologist David M. Raup. The “kill curve” (blue) of RAUP 1991 was originally fit to the Cretaceous – Palaeogene impact data (60% of species wiped out with the Chicxulub crater of about 180 kilometer in diameter), and it predicted that much smaller impacts should cause significant extinctions. However, when the late Eocene impacts (which caused almost no extinctions) are plotted, the “kill curve” takes a different, S-like shape, and suggests that only the impacts above a certain threshold value have the potential to cause mass extinctions. But even one of the best studied event – the Chicxulub-impact – is not unequivocal.

Bibliography:

PROTHERO, D. (2006): After the Dinosaurs: The Age of Mammals (Life of the Past). Indiana University Press: 384

David Bressan About the Author: Freelance geologist dealing with quaternary outcrops interested in the history and the development of geological concepts through time. Follow on Twitter @David_Bressan.

The views expressed are those of the author and are not necessarily those of Scientific American.



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  1. 1. dwbd 9:57 pm 02/17/2013

    Very interesting. There was also the comet that is believed to have impacted Northern Canada about 10,000 years ago and may have caused the extinction of many large mammals in North America like Mastodons & Saber-Tooth Tigers as well as the Clovis people.

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  2. 2. jtdwyer 2:18 am 02/18/2013

    As I understand, there’s very few 250 million year old rock formations that can be evaluated for extraterrestrial elements.

    There is most likely a minimum impact that can produce global effects (i.e. injecting sufficient material into the stratosphere, etc.) – regionally restricted effects could produce at most the extinction of species that are specific to the affected region.

    The recent dating of the Chicxulub impact to 66 million years ago puts it 1 million years away from the initial eruption of the approximately antipodal massive Deccan Traps flood basalt lava flows, dated from marine sediments. The Indian subcontinent is comprised almost entirely of The Indian Shield that is highly impervious to such enormous geologic events – the Deccan Traps eruption occurred roughly in the middle of the Indian Shield.

    Meanwhile, the Siberian Traps are recognized as having significantly contributed to the end-Permian extinction. There are candidate antipodal craters on the coast of Antarctica and Australia that may relate to that event.

    A giant asteroid impact imparts enormous kinetic energy directed towards the Earth’s interior. While it’s thought that flood basalt eruptions may be produced by the sudden emergence of a deep mantle plume. While mantle plumes have been associated with the creation of trailing island chains, such as the Hawaiian, and even supervolcano caldera, the continental scale Siberian and Deccan Traps would seem to require some more fundamental source of large scale energy flow directed from the Earth’s interior. Following a series of periodic eruptions with a discrete start date, these enormous continental scale plumes seem to largely release all of their energy an either cease or greatly diminish their volcanic effects. Please see
    http://en.wikipedia.org/wiki/Mantle_plume#The_impact_hypothesis

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  3. 3. gizmowiz 10:24 am 02/18/2013

    Usually an author will include a KEY to indicate what each line is. What are the blue, green and red lines supposed to indicate–this is not clear without the key!!

    Dumb.

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  4. 4. jtdwyer 10:48 am 02/18/2013

    David Bressan – While your linked posting, http://blogs.scientificamerican.com/history-of-geology/2011/11/10/the-devils-tail-what-the-fossils-say/
    raises many issues with the fossil record regarding the specific assumptions regarding how various groups were killed off, can’t it generally be said that species’ survival was strongly correlated with their ability to escape the atmosphere? In other words, those that survived were mostly those that could survive in water or burrow underground, along with a few unexplained exceptions such as birds & perhaps reptiles?

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  5. 5. Staten-John 2:14 pm 02/18/2013

    I can’t comment on the Sudbury nor Vredefort impacts because they are very old but all mass extinctions can be explained by the Gravity Theory of Mass Extinction:
    http://www.dinoextinct.com/page13.pdf

    When mass extinctions are studied, the following 3 conditions are present:
    1. Large fauna, both terrestrial and marine become extinct.
    2. A massive drop in sea level occurs.
    3. Flood basalt volcanism initiates after the extinctions occur.

    The above mentioned theory is able to explain why these characteristics occur with every mass extinction.

    BTW, the impact at the end-Cretaceous was not antipodal to the Deccan Traps. Continental distribution then was very different from what it is today.

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  6. 6. jtdwyer 8:59 pm 02/18/2013

    Staten-John,
    Since you cited no sources for your declaration that “the impact at the end-Cretaceous was not antipodal to the Deccan Traps”, I have to presume that you’re referring to a simulation model study produced in 2011. However, while your statement accurately reflects the news report headlines, the research is far less definitive.

    “Impact study: Princeton model shows fallout of a giant meteorite strike,”
    http://www.princeton.edu/main/news/archive/S31/90/32S94/
    The study’s lead author Matthias Meschede states:
    “Our model shows that because the Earth is elliptical and its surface is heterogeneous those waves travel with different speeds in different areas, changing where the waves end up on the other side of the world and the waves’ amplitude when they get there. These waves also are influenced by the interior. The effect on the opposite side is a result of the complete structure.”
    “Our measurements indicate that a Chicxulub-sized impact alone would be too small to cause such a large volcanic eruption as what occurred at the Deccan Traps.”

    “A Smaller Ka-Boom! Chicxulub Impact Did Not Cause Deccan Traps,”
    http://palaeoblog.blogspot.com/2011/10/smaller-ka-boom-chicxulub-impact-did.html

    “Antipodal focusing of seismic waves due to large meteorite impacts on Earth,”
    http://dx.doi.org/10.1111/j.1365-246X.2011.05170.x
    http://gji.oxfordjournals.org/content/187/1/529.full.pdf+html

    The research report states:
    “… Since our 3-D model is based on today’s Earth’s structure, the impact location and corresponding antipode location are inaccurate with respect to past continent configurations. The impact location was chosen to mimic Chicxulub’s impact location with respect to the Eurasian and American landmasses, which were closer together 65 Ma. The chosen position therefore deviates from the present-day crater position in the Yucatan and lies in the Atlantic Ocean (25◦N, 63◦W). The ancient antipode position was north of Australia and not on the continent, as in our simulations. We therefore merely use the simulations to demonstrate the effects of today’s heterogeneities, which should be comparable to the influence of ancient Earth’s structure.”

    The very admirably detailed model of the Earth represents the current structure: I presume to in some way better represent ancient internal features, the researchers began by choosing to significantly offset the point of impact eastward from the Chicxulub site, in the Caribbean region perhaps East of the Dominican Republic, as shown in Fig. 4 of the research report.

    The model did consider the reflectivity of both the solid and liquid iron core. As a result of all the parameters representing the dynamics of seismic waves propagated through the Earth’s interior, the antipodal site identified was not the point directly opposite the chosen impact point: interestingly, it was offset from the point directly opposing the impact point by a distance comparable to the ancient offset of India, as shown in the Princeton press release referenced above.

    At any rate, while this exceedingly complex model attempts to consider all factors that might influence the propagation of high energy seismic waves, the simple fact is that the models results cannot be verified against any actual data, much less validated against actual results of the Chicxulub impact.

    The established facts are that an enormous meteorite did produce a crater in the Chicxulub region on the coast of the Yucatan peninsula, now dated 66 million years ago, and that the enormous Deccan Traps flood basalt eruptions began 67 million years ago. If we presume that a meteorite impact of the magnitude of the Chicxulub impact occurs every 184 million years (assuming that a greater impact might have occurred at the end of the Permian period ~250 million years ago, 250-66 million years) and flood basalt lava flow eruptions the magnitude of the Deccan Traps occurs every 183 million years ago (since the Siberian Traps occurred ~250 MA), as I understand, the probability that two such causally unrelated events would occur within 1 million years of each other would be about 1/33,672. The extremely low probability of such random, unrelated coincidences argues that a causal relationship for the two events should be extensively investigated.

    While the Meschede et al. study is an admirable analysis, the extreme complexity of the model required to simulate such complex conditions and the inability to validate model results against actual events indicate that these researcher’s results cannot be considered definitive in determining the results produced by such large asteroid impacts.

    BTW, the Cretaceous–Paleogene extinction event is thought to have occurred about 66 million year ago, while the Deccan Traps eruptions are currently thought to have begun 67 MA – preceding, not following, the extinction event.

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  7. 7. rugeirn 8:36 pm 02/22/2013

    Here’s what I’ve never understood about meteor-impact theories of mass extinction.

    Various impact events happened. I get that. And they caused profound ecological effects. I get that too. But the extinctions take place over periods of millions of years. Even if we’re only talking one or two million years, that’s still a very long time. We’re looking at hundreds of generations of the species involved. How can we say that the impact event was “the cause?” Doesn’t the sheer time scale involved require that many other factors be involved?

    Where can one find rigorous, critical, impartial analysis of this?

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  8. 8. Knyaz 10:15 am 02/28/2013

    Из-за изменения формы Земли произошло нарушение (изменились скорость вращения Земли вокруг своей оси и угловой наклон) равновесия в системе Земля-Луна и Луна подошла на такое расстояние когда Луна оказалась в области тяготения Земли (не путать с притяжением)не доходя до точки Лагранжа Луна обмениваясь метеоритными ударами с Землей (лунный грунт найден на Земле,земной грунт на Луне а лунный лёд это земная атмосфера)сменила географические полюса одновременно с Землей (смену географических полюсов Луны доказали сотрудники парижского Института Физики Земли Mark Wieczorek and Matthien Le Feuvere)удалилась от Земли.Такие события произошли во время лунного затмения.В настоящее время происходит приближение подобного сценария экстремальное изменение погоды это показатель изменения климата (человек,CO2 и метан ускорители изменения климата),изменение климата это показатель изменения альбедо Земли,изменение альбедо показатель изменения процессов в ядре Земли(bit.Ly/LW22KOJ).Изменение процессов с ядре Земли деформируют земную кору изнутри изменяя форму Земли (смотрите в интернете изменение формы Земли картинки “Земля как картошка”).То,что уже происходило вероятно произойдет снова во время лунного затмения в северном полушарии Земли.Солнце превратится во тьму и луна-в кровь,прежде чем наступит день Господень,великий и страшный.Иоиль 2,31.И сказал мне Господь;от севера откроется бедствие на всех обитателей сей земли.Иремия 1,14.

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