for National Geographic News
Comets slamming into the Earth may be responsible for both the birth and the death of the dinosaur era, an international group of researchers report.
There is a considerable amount of evidence that a bolide (a comet or asteroid) collision with Earth triggered the end of the dinosaur era 65 million years ago.
An international team of scientists has assembled a compelling collection of evidence that a giant ball of ice, rock, and gases smashed into the supercontinent Pangaea 200 million years ago, ending the Triassic era and beginning the Jurassic. The impact was devastating to ocean life, and more than half of land-based species disappeared. Once the dust had cleared, dinosaurs began their 135 million year reign as the planet's dominant life-form.
"We have been able to show for the first time that the transition between Triassic life-forms to Jurassic life-forms occurred in a geological blink of an eye," said Paul Olsen, a geologist at the Lamont-Doherty Earth Observatory of Columbia University. "The change was associated with an iridium anomaly suggesting the cause was the result of a giant impact of an extraterrestrial body."
Crocodile relatives were dominant during the Triassic, while dinosaurs were dominant in the Jurassic. Olsen is the lead author of the study published in the May 17 issue of the journal Science.
"Different lines of evidence, including dinosaur footprints, skeletal remains, and a spike in iridium levels exactly at the change in plant spores from the strata that mark the Triassic-Jurassic boundary, are all suggestive that a disaster befell the land and it may have been a comet or an asteroid," said Dennis V. Kent, a geologist at Rutgers University and a co-author of the study.
Piecing Together the Evidence
Since the first appearance of life on the planet around 4.6 billion years ago, there have been at least five mass extinction events, when 50 percent or more of the species on Earth disappeared. On the other side of these biodiversity crashes, new life-forms appear and thrive. The mass extinction of the dinosaurs 65 million years ago, for instance, lead to the age of mammals.
"The disappearance of one set of plants and fossils, and the appearance of new forms of life, are what characterize geological boundaries," said co-author Hans-Dieter Sues, a paleobiologist at the Royal Ontario Museum in Canada.
The Earth was still one big landmass 200 million years ago, a supercontinent called Pangaea that was getting ready to break apart. As the Earth's crust stretched and thinned, great rift valleys appeared. One, called the Newark Basin, was formed just prior to the separation of North America from Europe and Africa. Stretching through parts of New York, New Jersey, and Pennsylvania, it is a geological treasure trove. The researchers examined footprints, bones, and plant spores at 70 locations in the Newark Basin.
"The Triassic-Jurassic boundary is identified very precisely by a fern spike," said Dennis V. Kent, a geologist at Rutgers University and a co-author of the study. "An increase in the spores of ferns is indicative of an ecological calamity. Ferns are the first plant to invade and colonize when everything else has been wiped out. You can see a similar phenomenon today at Mt. St. Helens after the volcano erupted."
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