A Permian anteosaurus: He feels vaguely nervous, and oddly sweaty. (image courtesy of Wikipedia Commons)65 million years ago something very sad happened. Well, it was sad for the dinosaurs, because they all died, but great for us mammals. Here – I’ve written a little play about it:
Scene 1
Dinosaur 1: Hey, have you noticed that there seem to be a lot less of us these days?
Dinosaur 2: What? I don’t know. Why?
Dinosaur 1: Probably just my imagination. Forget about it.
Dinosaur 2: …
Dinosaur 1: Hey, what’s that thing up there?
Dinosaur 2: We call it the sun.
Dinosaur 1: No, that thing – it’s getting bigger, I think.
Dinosaur 2: Oh, not to change the subject, but did you watch Entourage last nigh*
Scene 2
(fiery, dusty chaos)
Scene 3
Rodent-like mammal: Yes!
The End
Anyway, the extinction at the end of the Mesozoic (dinosaur times) was a big deal. But, dramatic as it likely was, it was nothing compared to the extinction at the beginning of the Mesozoic.
Before the dinosaurs existed, the world was ruled by a different kind of animal, the therapsids, or “mammal-like reptiles.” These ranged from little rat like guys to huge fanged and clawed lion-like creatures. About 250 million years ago, though, at the end of the Permian period, there was an extinction event way bigger than the one that would eventually kill all the dinosaurs.
The Permian extinction killed off 90% of all the life on the planet, both on land and in the oceans. Life as we know it just squeaked by complete annihilation. The thing is, scientists still aren’t sure exactly what initiated the extinction. Whatever it was, it caused massive amounts of carbon dioxide, and other greenhouse gases to be released into the atmosphere. The earth would have gotten warmer and warmer, the oceans would have become acidic, and by the time things got back to normal, almost every species on the planet had died out.
Jonathan Payne, a paleobiologist at Stanford, is investigating one of the possible causes of the extinction – a massive volcanic eruption occurring at the end of the Permian. This eruption was the larger than any other that has happened in the last 600 million years, and it spread a four-mile thick sheet of basalt the size of the continental US over Asia. Along with the poisonous gases spewed by the volcano itself, it is believed that the spreading magma may have heated the coal-rich strata near the eruption and released vast amounts of carbon dioxide into the atmosphere. Then, you know, the whole horrible global warming and acidic oceans thing.
Fortunately, for all our CO2 production, we aren’t yet in the Permian extinction league of global warming gases. Still, Payne is comparing contemporary signs of global warming to those leading up to the Permian event. For example, under increasing environmental stresses, coral colonies tend to bleach (as algae leaves the reefs). Researchers will be examining fossilized coral colonies from the end of the Permian to see how they reacted to the changing environment. "We hope to reconcile the short-term processes we observe operating in the modern world with the very long time scales seen in the geologic record," says a researcher in Payne’s lab. If the analogy works, we could better understand the processes of past environmental change, as well as the potential future effects of the environmental changes that are occurring today.
My own theory regarding the Permian extinction largely focuses on the refusal of therapsis to carpool, and their insistence on driving larger vehicles than they really needed (cyconodonts were notorious SUV lovers). Unfortunately, this is extremely difficult to verify in the fossil record. I chalk this up to the poor preservation of pre-Triassic GM products, or, possibly, to the fact that therapsids had adapted to finding (and then losing) well concealed parking spots (they were, after all, much more primitive than us).
Tags :
Meteor Crater near Winslow, AZ: This crater formed when a meteor collided with Earth about 50,000 years ago. It is approximately 3/4 mile in diameter and 650 feet deep.
Courtesy Mark Ryan
A 300 mile wide crater (bigger than Ohio) has been detected beneath a half-mile of ice in Anartica. This crater is twice as big as the one thought to have killed the dinosaurs. Reseachers believe the impact may have broken up the Gondwana supercontinent, pushing what is now Australia northward.
Two separate data sets were combined to understand more about this impact. Radar to detect a crater, and gravity measurements to detect a mass concentration, or "mascon" in the same place. When a large mass slams into the earth, there is a rebound of mantle material up into the earth's crust creating a bump or mascon..
"On the moon, you can look at craters, and the mascons are still there," von Frese said. "But on Earth, it's unusual to find mascons, because the planet is geologically active. The interior eventually recovers and the mascon goes away." He cited the very large and much older Vredefort crater in South Africa that must have once had a mascon, but no evidence of it can be seen now.
"Based on what we know about the geologic history of the region, this Wilkes Land mascon formed recently by geologic standards -- probably about 250 million years ago," he said. "In another half a billion years, the Wilkes Land mascon will probably disappear, too." Ralph von Frese, a professor of geological sciences at Ohio State University
The Permian-Triassic extinction about 250 million years ago, when almost all animal life on Earth died out, may have resulted from this impact.
Not all scientists agree, however
Scientists contacted by news@nature.com say they are sceptical, as no signs of such an enormous impact have been found in other, well-studied areas of Antarctica. Jane Francis, a geologist at the University of Leeds says, "That sequence has been worked on before, and no one has found evidence to support a massive impact like this," Paul Wignall, a palaeontologist at the University of Leeds, UK, who studies mass-extinction events says that few scientists will be convinced by the hypothesis until the team can precisely date their crater directly, and find rocks there that have been altered by the searing heat of the explosion.
Most think that the extinction started when a vast volcanic eruption released huge amounts of gas, including sulphur dioxide and carbon dioxide, into the atmosphere, causing acid rain and greenhouse warming. Von Frese notes that the explanations aren't mutually exclusive: the shockwaves from a huge impact could have travelled through the planet to trigger the eruptions in Siberia, delivering a devastating combination of disasters.
Too much ice covers the putative crater for a drilling expedition. But Von Frese hopes to make a research trip to Antarctica to look for rocks at the base of the ice sheet along the continent's coast that could attest to an impact.
Sources:
NatureNews
physorg
space
BBCnews
Yahoo news
Subscribe
I want to learn about
Science Buzz is supported by the National Science Foundation.Copyright © Science Museum of Minnesota, 2004-2010, except where noted.
Add a new comment