Earth's largest environmental catastrophe 250 million years ago studied

Sep 14, 2011
Siberian Traps near lake Lama, Norilsk region. © N.A. Krivolutskaya

The eruption of giant masses of magma in Siberia 250 million years ago led to the Permo-Triassic mass extinction when more than 90 % of all species became extinct. An international team including geodynamic modelers from the GFZ German Research Centre for Geosciences together with geochemists from the J. Fourier University of Grenoble, the Max Plank Institute in Mainz, and Vernadsky-, Schmidt- and Sobolev-Institutes of the Russian Academy of Sciences report on a new idea with respect to the origin of the Siberian eruptions and their relation to the mass extinction in the recent issue of Nature.

Large Igneous Provinces (LIPs) are huge accumulations of volcanic rock at the Earth's surface. Within short geological time spans of often less than one million years their eruptions cover areas of several hundred thousand square kilometres with up to 4 kilometers thick lava flows. The Siberian Traps are considered the largest continental LIP.

A widely accepted idea is that LIPs originate through melting within thermal plumes, a term applied to giant mushroom-shaped volumes of plastic mantle material that rise from the base of the mantle to the lithosphere, the Earth's rigid outer shell. The high buoyancy of purely thermal mantle plumes, however, should cause kilometer-scale uplift of the lithosphere above the plume head, but such uplift is not always present. Moreover, estimates of magmatic degassing from many LIPs are considered insufficient to trigger climatic crises. The team of scientists presents a numerical model and new geochemical data with which unresolved questions can now be answered.

Animated model of the lithosphere destruction by the mantle plume. (Click 'Enlarge')

They suggest that the Siberian mantle plume contained a large fraction of about 15 percent of recycled ; i.e. the crust that had long before been subducted into the deep mantle and then, through the hot mantle plume, brought back to the Earth's lithosphere. This recycled oceanic crust was present in the plume as eclogite, a very dense rock which made the hot less buoyant. For this reason the impingement of the plume caused negligible uplift of the lithosphere. The recycled crustal material melts at much lower temperatures than the normal mantle material peridotite, and therefore the plume generated exceptionally large amounts of magmas and was able to destroy the thick Siberian thermally, chemically and mechanically during a very short period of only a few hundred thousand years. During this process, the recycled crust, being exceptionally rich in volatiles such as CO2 and halogens, degassed and liberated gases that passed through the Earth crust into the atmosphere to trigger the mass extinction. The model predicts that the should have occurred before the main magmatic eruptions. Though based on sparse available data, this prediction seems to be valid for many LIPs.

Explore further: Bridgmanite: World's most abundant mineral finally named

More information: Stephan V. Sobolev, Alexander V. Sobolev, Dmitry V. Kuzmin et al., Linking mantle plumes, large igneous provinces and environmental catastrophes, Nature, vol. 477, p. 312-316, 2011

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User comments : 9

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xpst
3 / 5 (2) Sep 14, 2011

An alternative theory is that huge coal beds in Siberia were burned by up-welling magma, thus releasing huge volumes of CO2. If the extinctions did precede the magma rise through the coal beds, that would indeed favor the outgassing theory.
Urgelt
not rated yet Sep 14, 2011
I suspect we're still groping for answers.

Might something deeper under the mantle have contributed to the formation of the mantle plume? After all, we don't see those happening every week (or every 250,000 years, actually).

If so, what could it have been?

We suspect there are abundant radioactive elements down there, heavy elements that are much rarer in the crust. Is it possible that a huge and sustained fission reaction ignited somewhere down near the core, dumped a higher amount of energy into the mantle and contributed to formation of a plume? Perhaps the plume subsided when the pocket of fission was exhausted?
Jonseer
1 / 5 (9) Sep 14, 2011
OH no this can't be right.

It's ALWAYS a giant impact.

Just ONE giant impact, based on an iridium layer which is the Imprecise before and after point of the time of impact.

The fact that the lack of precision could mean a million or so either way is just nothing to worry about,and that various creatures seem to survive without rhyme or reason is nothing to worry about.

Certainly nothing like a big volcanic eruption over thousands of years can't match a giant meteor for extinction. ;)

Yes ALWAYS a meteor impact. LOL
Jonseer
1 / 5 (5) Sep 14, 2011
One thing to keep in mind about volcanic eruptions back then people is the interior of the Earth was a lot hotter, and the crust significantly thinner, and the lava a lot less viscous than today.

As a result, the theory thus doesn't need as many extraordinary events to make it possible, though they could have happened regardless.
Ethelred
5 / 5 (4) Sep 14, 2011
No it was NOT ALWAYS an impact. There was little thought that an impact was involved until the Alvarez's did their work with the KT event where further exploration supported them.

There is still for an impact with the Permian extinction but is still weak. Geologists usually prefer a geological cause BUT the evidence for the KT impact is VERY strong. That impact implies that the Permian extinction could also be caused by an impact.

Basically it was either a bloody strange coincidence that the KT impact hit at just about the same time as the Deccan Traps started on pretty much the exact opposite side of the world or the impact triggered the geological event.

Since the Permian extinction occurred much farther in the past evidence for an impact will be harder to find assuming one was involved. Best guess is that if there was an impact it occurred in deep ocean water and that too makes evidence very hard to find.

Ethelred
Ethelred
5 / 5 (5) Sep 14, 2011
One thing to keep in mind about volcanic eruptions back then people is the interior of the Earth was a lot hotter
Got any evidence to support that?

The Permian was not that long ago in terms of heat. The main source of heat in the Earth's core is the same now as then and the Uranium has a rather long half life of 4.5 billion years. So the amount of heat should be similar to then and the Earth's crust has been forming for at least around 4 billion yeas since the hypothetical collision that formed the Moon. Longer if there was no such collision. Thus the crust should only be about a sixteenth thicker than 250 million years ago. The core and mantle temperature change should be about the same sixteenth.

Of course I could be missing something significant but that sixteenth should be fairly close unless I am.

Ethelred
Decimatus
not rated yet Sep 14, 2011
I have often wondered whether the giant caldera's of super volcanos, and even from this mantle plume could have been gaping wounds opened by extremely high velocity asteroids.

Many asteroids in our system are moving at a relatively docile 20-60k mph. Imagine we hit a meteroite storm that was moving from a different area on the galactic plane. The rocks and stars closer to the core, as well as farther from the core than us can be moving at potentially enourmous speeds compared to local objects.

Thus, if a rock comes flying in from out of the solar system at any significant fraction of the speed of light, say 1-5%, I can see it slamming all the way down into the mantle and causing thousands of years of mantle outflow.

Kind of a theory that covers both bases. Highly unlikely, but also highly devastating if it does happen.
Ethelred
4.5 / 5 (2) Sep 15, 2011
The Yellowstone caldera, for instance, has predecessors across the North American continent so I don't think it could be from an impact. Come to think of it if the Deccan and Siberian Traps are supposed to be from a plume why is there only the one outpouring each unlike many other plumes.

Ethelred
vidar_lund
not rated yet Sep 15, 2011
Come to think of it if the Deccan and Siberian Traps are supposed to be from a plume why is there only the one outpouring each unlike many other plumes.

Ethelred

The Deccan Traps plume is believed to still be active, http://en.wikiped..._hotspot

Regarding deep impacts by super fast asteroids or comets from outside of the solar system this is extremely unlikely. The asteroids we see are bound to the solar system and the same will be the case for other stars (their asteroids will be bound as well). A supernova may be able to blast objects into space but it's very unlikely that such a stray bullet would hit earth.

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