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What Caused Dinosaur Extinction?New evidence shows that it was not only the Yucatan's meteorite |
By Stefan Anitei, Science Editor
31st of October 2006, 08:44 GMT
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New evidences suggest that the global mass extinction at the end of the Dinosaur Era might not have been produced by the single Chicxulub meteor impact, found in Yucatan peninsula (Southern Mexico), but by multiple meteor impacts, massive volcanism in India, and climate changes. "The Chicxulub impact may, in fact, have been the lesser and earlier of a series of meteors and volcanic eruptions that pounded life on Earth for more than 500,000 years," say Princeton University paleontologist Gerta Keller.
A later much larger impact 65.5 million years ago must have been the last straw, destroying the dinosaurs and with them two thirds of all world species at that time, like giant marine reptiles (plesiosaurs, mosasaurs), pterodactils (flying reptiles), ammonites (shelled squids), many primitive birds and mammals. "It's that impact - not Chicxulub - which left the famous extraterrestrial iridium layer found in rocks worldwide that marks the impact that finally ended the Age of Reptiles,"
Keller believes.
Chicxulub crater is nowadays half on land and half on the sea floor. Analysis of marine sediments from the crater, from a site in Texas along the Brazos River, and from outcrops in northeastern Mexico has showed that Chicxulub meteorite event took place 300,000 years before the mass extinction. "In all these localities we can analyze the marine microfossils in the sediments directly above and below the Chicxulub impact layer and cannot find any significant biotic effect," said Keller.
"We cannot attribute any specific extinctions to this impact. No one has ever published this critical survival story before".
Chicxulub - though violent - was followed by prolonged and gigantic eruptions of the Deccan Flood Basalts in India, as well as by climate change, and after all, a second large impact pushed the species towards the brink of extinction. The Deccan volcanism released during a period of more than a million years huge amounts of greenhouse gases into the atmosphere. "By the time Chicxulub struck, the oceans were already 3-4 degrees warmer, even at the bottom. On land it must have been 7-8 degrees warmer," says Keller.
"This greenhouse warming is well documented. The temperature rise was rapid, over about 20,000 years, and it stayed warm for about100,000 years, then cooled back to normal well before the mass extinction."
When Chicxulub meteorite hit, most species were suffering from heat stress, proved by dwarfing, growing less than half their normal size and reproducing through r strategy (many offspring to increase the chances for survival).
After the heat period, climate cooled back to normal, but most tropical species were already very vulnerable, with reduced populations. When the second large meteorite hit, it pushed them straight to extinction. Dinosaurs themselves can not help to directly elucidate what happened to them because "dinosaur fossils are few and far between," as Keller said. "We can only really study what happened to them by looking at microfossils because these little critters are everywhere at all times. In just a pinch of sediment we can tell you the age, the prevailing climate, the environment in which it was deposited and what happened."
The site of the final impact is still unknown. "There is some evidence that it may have hit in India, where a crater of about 500 kilometers in diameter is estimated and named Shiva by paleontologist Sankar Chatterjee from the Museum of Texas Tech University in Lubbock. The evidence for it, however, is not very compelling at this time."
"Chicxulub is one of thousands of impact craters on Earth's surface and in its subsurface," said H. Richard Lane, from the National Science Foundation (NSF) Division of Earth Sciences. "The evidence suggests that there is more to learn about what caused the major extinction event millions of years ago, and the demise of the dinosaurs at the end of the Cretaceous."
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User opinions: |
| Comment #1 by: Gemma (14) on 29 Feb 2008, 09:47 GMT |  reply to this comment | Personally, I think that what caused the dinosaur's sudden extinction is many affects including several asteroid collisions, volcanism and mammal competition. At the moment I'm doing my case study on 'What caused the extinction of the dinosaurs?' and I found this page really useful. I think there may have been an asteroid shower of some sort but, using the Tunguska Fireball as an example, some evidence would be microscopic! The Tunguska Fireball was an asteroid which flattened a forest and killed many animals within that forest but, the asteroid didn't cause a crater and the only evidence that the scientists could find of it being an asteroid is microscopic evidence! I also think that after this, there was a sudden climate change and volcanos began erupting everywhere which is why there are flood basalts in India and Siberia dating back to the correct time. But, because the dinosaurs began dying out before the major impact(s) I think it would have been the volcano that erupted in Siberia dating back just before the major extinction of the dinosaurs and mammal competition for food. Because of continental drift, the dinosaurs may have been separated from their food sources which could have caused them to die of starvation. I am really interested in what killed the dinosaurs so I hope we get the mystery solved soon!! And thanks for all the information on this site as it really helped me with my coursework!! =) |
| Comment #2 by: robert cooper on 04 Apr 2008, 21:46 GMT | reply to this comment | personaly i think the dinosaurs died out because:an astroied
hit astraillia [the middle of the earth],the blast would have killed
everything for miles around after that the there was a random change in the climate the type of plants were poisonos killing the
plant eaters the meat eaters would eat the last of the carcus's
making them die of hunger |
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