Permian crater found?

Factual Questions
1

That’s the claim in this article in the April 15th edition of Earth and Planetary Science Letters . This 75-mile crater, combined with a 25-miler found earlier in Brazil, seem on first blush to line up nicely with the Permian mass extinction event.

What do Dopers think about this? And if in fact the Permian was just another routine meteor/asteroid extinction, what’s the current scorecard of mass extinction causes from on-world events such as gas poisoning (oxygen, for example) and climate change?

2

The last time I paid attention to this it seemed that the geochemists, geophysicists, astronomers and popular press were sold on the idea of asteroid collisions as the cause of extinctions while the paleontologists and biologists/ecologists disagreed, mainly because the evidence was not there.

There is something unsettling about searching for a large crater for every extinction event or looking for an extinction event for every large crater found.

Has anyone ever proposed an ecological model that shows why some species survive these asteroid collision events and some don’t? I assume that the proponents of the asteroids-cause-extinctions believe something like a “nuclear winter” scenario occurs.

Is there any pattern to the animals that survive? If the surviving animals all showed an ability to thrive on carrion (probably a little gamey after the first decade or two), were all able to shiver thru the cold, or were all small or quick enough to dodge supersonic shock waves, I would feel more comfortable with the idea. Or if certain regions were spared (like the other side of the planet) and it could be determined that the inhabitants of those areas were able to go forth and colonize the devastated areas.

That does not seem to be what happened? Why would birds (whose modern descendants are pretty sensitive) survive the K-T event and ammonites and diatoms die off? Post-collision conditions need to explain why some were spared and some not.

My own personal guess, for what it is worth, is that extinctions are caused by massive, massive volcanic outpouring, both aerial and marine, causing widespread poisoning. There is still a problem with selective survival, but volcanism can be more widespread, longer duration, and more massive than an ateroid collision.

Remember the old Gaia hypothesis? Part of it was that the Earth could buffer or absorb ecological change or punishment. An asteroid event just seems to small to upset the balance.

3

Url=http://130.132.143.21/ynhti/curriculum/units/1996/6/96.06.03.x.html#h]Extinction and the Fossil Record

4

Let’s try that link again.
http://130.132.143.21/ynhti/curriculum/units/1996/6/96.06.03.x.html#h

5

[QUOTE]
Originally posted by mipsman:
[My own personal guess, for what it is worth, is that extinctions are caused by massive, massive volcanic outpouring, both aerial and marine, causing widespread poisoning. There is still a problem with selective survival, but volcanism can be more widespread, longer duration, and more massive than an ateroid collision.
Such volcanic eruptions should have left ample evidence of their occurance at the K-T boundry, akin to the iridium layer.

6

First, it’s not such a clear distinction. Count me as a geochemist that is skeptical when it comes to the hypothesis that asteroids are the primary agent of extinction. Astrophysicists, such as Louis and Walter Alvarez (the formulators of the “Alvarez Hypothesis”–the Ir-layer at the K-T boundary equals asteroid-impact induced extinction hypothesis), as a whole do not entertain alternate theories, but you might be able to see a little bias for a pet hypothesis there. Paleontologists seem to be more evenly split. Guys like me have an opinion, but it’s not our realm.

I agree. The geologic record is full of extinctions. In fact, the whole geologic time scale is deliniated based on faunal assemblages; i.e., the Cambrian is defined based on some critters that aren’t seen in the Ordovician. Why? 'Cause they went EXTINCT! Before we worry about the BIG causes of extinction, we’ve got to ask the basic question: why do some critters go extinct and others don’t? And, really, the answer is simple. When an environment changes, organisms that can adapt do; organisms that can’t adapt don’t, and gradually become extinct. On a modern scale, consider urban development. Some poor creature that has a very restricted habitat and/or diet may be deprived of those things; if it can’t adapt (find a new home and/or diet), it will die. Animals that can adapt (Squirels, Racoons, Pigeons, etc.) thrive.

So, a change in environment causes extinction of only those critters that cannot adapt. What causes environmental change? Tons of things; the geologic record is full of good reasons: tectonics (plate motion changes ocean currents that exert strong control on climate), volcanoes (enough of 'em erupting enough stuff), and–yes–even asteroids (the rarest of events). Consider the Eo-Oligocene, the largest mass extinction since the K-T. It follows a period of time that saw widespread, massive volcanism in the American west. The Oligocene was the start of a cool-down that cummulated in the Pleistocene Ice Ages, that we’re only now (over the past 10 ka) starting to recover from.

Not really, which is why I’m suspicious of a Permio-Triassic impact as the instigator of this event. Thecodonts, ancestral dinos, evolved during the Permian and survived the extinction while poor bastards like Trilobites kicked the bucket. Yet, the dinos–not much different from Papa Thecodont, all died at the end of the Cretaceous, along with such critters at the Ammonites and Rudistds (while Frogs, most Mammals, etc. were left alone). What happened during the Permian? Pangaea came together. What happened during the Cretaceous? Pangaea had completely split apart (this had begun in the Jurassic). Sounds to me like a tectonic control shouldn’t be discarded.

Now, there is no denying that asteroid impacts happen; there is ample physical evidence for that. But it sure isn’t a good one-size-fits-all model for mass extinction. Extinctions happen because environments change and some animals just can’t adapt. And there’s a bunch of things that can cause the environment to change.

7

NOW I remember what else I was going to mention!

The idea that “all” the dinosaurs were killed at the end of the Cretaceous is a fallacy. Only the dinos that were left after earlier extinction events at the end of the Jurassic and sometime in the Early Cretaceous went extinct, and it’s generally agreed that the J-K and Early K extinction events were NOT asteroid-controlled. To address your point, during these events, Sauropods were wiped out of North America, but survived in South America. Only in the latest K do we see them return to North America. Likewise, the K-T even killed Marsupials everywhere except Australia. Since, by the Tertiary, Australia had already divorced itself from the rest of Pangaea, Koalas never had the chance to migrate very far.

8

Pantellerite, I don’t think this is accurate:

Unless you think they swam there. :stuck_out_tongue: Marsupials inhabit South America, North America and Africa.

See http://www.geobop.com/Mammals/Marsupialia/2.htm

9

Oops. Sorry for the broad, and inaccurate, generalization. What I was trying to point out was that most marsupials (except for a few in scattered locations) went extinct at the end of the Cretaceous. Similarly, after the Early Cretaceous extinction event, most sauropods (except for a few in scattered locations) went extinct.

10

Eh, the only thing that fascinates me in all of this is the Burgess Shale.

Wiwaxia rules the universe!! :slight_smile:

[/hijack]

All I wanna do is to thank you, even though I don’t know who you are…

11

There is still some doubt about the impact theories for other extinction events–most of the boundary layers do not have an enhanced layer like the iridium layer in the KT boundary. Even the referenced article is weak–notice that the last sentence of the abstract says “the lack of Triassic fossils in the crater fill favours a late Triassic age.” That would remove it as a culprit in the PT extinction.

Pantellerite

The Alvarezes were not astrophysicists.

Such evidence is very well known. Even at the PT boundary. And that is the reason that the controversy continues.

rocks

12

ISTR reading that astronomers and geologists were trying to find a periodicity for “collision extinctions” in the fossil record, and using that to calculate the orbit of a possible companion star to the Sun.

In other words:

If asteroid or cometary impacts cause extinctions, and

If these impacts occur on a more or less regular schedule, then

Maybe there’s a companion star with a highly elliptical orbit which perturbs Oort Cloud objects and sends them raining down on the inner solar system every few million years.

I don’t think any periodicity has been established, and I hope not too many scientists take this hypothesis seriously.

On On

13

You mean the Americas and Antarctica (previously), not Africa. Even your link says nothing about marsupials in Africa.

On On

14

Pantellerite said:

I don’t think this is correct either. AFAIK, marsupial extinctions in South America were primarily caused by competition with placental mammals from North America. Antartic marsupial extinctions occurred because of climate change. Australia was spared because of their isolation. I don’t know of any evidence supporting the hypothesis that massive marsupial extinctions happened at the KT boundary. Do you?

See http://www.biosci.ohio-state.edu/~zoology/eeob405/lab_9_q07.html

Five:

No, I mean Africa (see the elephant shrew). The referenced link does provide info about it, albeit on a separate page. Antartica certainly had them too, as I mentioned above, but they presumably went extinct much later than the KT extinction event.

15

While I don’t advocate a priori discarding any possible mechanism, isn’t a problem with tectonic causes of extinctions that any changes will happen gradually, giving time to adapt? A series of massive eruptions, or a large meteorite, are both quick changes, which can make adaptaion or relocation difficult.

It is too clear, and so it is hard to see.

16

I went back to the site and found the info about the elephant shrew. It’s a placental mammal, and even under the “Old World Marsupials” section of the Marsupials page there’s no mention of Africa.

On On

17

OK, as a planetary scientist (albeit one who’s away from his references right now), I’m going to have to stick up for asteroid impacts as the instigator of at_least the K-T extinction.

As the K-T boundary is probed with greater and greater resolution, it becomes more evident that that extinction occurs immediately, not gradually. Numerical modeling of the climate changes that would be created in an impact of the size of Chixculub would be enormous. Much of the controversy seems to be whether the CO2 and SO2 released into the atmosphere due to the specific mineralogy of the Yucatan made this impact particularly deadly or whether it would’ve been that deadly anyhow. Ejecta from the impact is found all the way from Haiti to Colorado to Italy. If the planetary science community has consensus about anything (and it doesn’t have consensus about much), it’s that the K-T extinction was instigated by an impact.

Naturally, then, the simplest explanation for all major extinctions (in the Occam’s Razor sense) is that they were caused by large impacts. It may not be the correct explanation, but it’s the natural place to start. Asteroid/Comet impacts of the right size occur on the right timescales, they have the power to create mass extinctions, and they’ve been implicated in the most popularly famous event. Looking for a Permian impact is the obvious next step.

Whether extinctions happen periodically or not is another question. I think most believe they don’t, but there’s very little data since the Earth wipes out its craters in relatively short order. If we could date all the craters on the Moon, though, we’d quickly see whether there’s a cycle.
-Andy

18

Five:

Your right, of course. Evidently I was misreading Macroscelididea as Marsupialia (don’t ask why). I’m glad you pointed that out, because I was having trouble envisioning how just that marsupial would end up in Africa if they originated in South America/Australia/Antarctica or North America.

19

Here’s a cite. From Dinosaurs: the textbook by Spencer G. Lucas (New Mexico Museum of Natural History, UNM), c.2000, McGraw-Hill. Page 230:

And, okay, so Luis Alvarez isn’t an astrophysicist… just a plain ol’ physicist (although Walter is a Geologist–I stand corrected).

asrivkin adds:

Maybe there is consensus amongst you guys, but it’s still a debate amongst those of us looking at the Earth. Two brief points:

  1. To quote Robert Bakker, “What about the frogs?” The highly selective nature of the K-T extinction makes many doubt the impact of the impact. Why Dinosaurs, but not frogs or crocodiles? Why ammonites? Why not birds? Recall also that by the terminal K event, most dinosaur species had been extinct since the EARLIEST Cretaceous.
  2. There is ample evidence that several of the organisms that were done away with at the end of the Cretaceous had been gradually going extinct throught the Cretaceous, like the ammonites. With dinos, the evidence is more contradictory, mostly because of sparse physical evidence. The Hell Creek Formaton (Maastrichtian) in Montana shows a very marked decrease in dino diversity from the bottom to the top.

I won’t disagree that a K-T impact happened and had a profound effect–perhaps on “finishing off” the dinos. But did it instiage the extiction? I doubt it.

20

Pantellerite:

I think your cite is supporting my position. I don’t deny that some of the marsupials went extinct during the KT event. Any species living near the impact crater would likely be affected. I take issue with your contention that most marsupials went extinct.

I don’t know why my above post is dated 04-29-2000 12:04 AM. It was originally right after Five’s post of 04-28-2000 11:41 AM before the board’s software conversion.