It is possible that several collisions of celestial objects with the Earth, and not one collision, caused the extinction of the dinosaurs 65 million years ago
William Broad
For more than a decade, most scientists believed that the extinction of the dinosaurs was the result of a single event: a gigantic object from space collided with the Earth and caused an explosion with the power of a hundred million hydrogen bombs. This collision, according to information, ignited huge fires and caused the formation of a compressed dust cloud, which blocked the sun's rays and caused the temperature on Earth to drop.
This theory was strengthened in 1991 after the discovery of a crater near the tip of the Yucatan Peninsula in Mexico. The age of the mighty underwater abyss that stretches over 180 km from lip to lip has been estimated at 65 million years; That is, it was opened at the time when the dinosaurs became extinct.
Recent findings complicate the picture a bit. Scientists in Ukraine have discovered that a crater smaller than the Yucatan crater, located in the Tiasmin River Basin in the east of the country, has been incorrectly dated and its true age is 65 million years. In addition, a team of British researchers recently discovered a crater at the bottom of the North Sea, Silverpit, which extends over 20 km and also dates to the same period.
These findings support the belief that deadly objects from space sometimes arrived in pairs and even in swarms. Such a theory may explain why the picture that emerges from the fossils is of species getting weaker and weaker until a final blow wipes them out completely.
"It's so clear," said Dr. Greta Keller, a geologist and paleontologist at Princeton University. "In recent years, a huge amount of new information has accumulated, indicating multiple conflicts." Keller claims that many researchers have based their reputations on the idea of a single catastrophe that brought the end of the dinosaur age, and they have difficulty accepting the new evidence. "It's hard to say goodbye to old ideas," she said.
Her research, Keller added, raises the possibility that, in fact, there are multiple collisions. The study casts doubt on whether the collision that created the Chicxulub Crater in the Yucatan sealed the fate of the dinosaurs. According to her, the fatal blow "has not yet been found".
The debate urges scientists around the world to look for more craters and to re-evaluate the age of craters that have already been discovered, looking for clues to a great catastrophe at the end of the Cretaceous era, which resulted in the extinction of thousands of species - not only dinosaurs, but also plants, fish and plankton. "There are more than 170 known craters on Earth, and we only know the exact age of about half of them," said Dr. Simon Kelly of the Open University in Great Britain, who discovered the dating error of the crater in Ukraine with Dr. Eugene Gorov of the Institute Geological of Ukraine.
Even in the US, Kelly said, some craters have been dated incorrectly. "In the UK we have a saying, 'You wait an hour for a bus, then three come at the same time,'" Kelly said. "Maybe the injuries happened in a similar way."
The idea that a giant invader from outer space caused the death of the dinosaurs was put forward in 1980 by Dr. Luis Alvarez, his son Dr. Walter Alvarez, and their colleagues from the University of California at Berkeley. The idea was initially received with skepticism, but after a while it became the accepted opinion.
In his 1997 book, "Tyrannosaurus Rex and the Crater of Doom", Walter Alvarez claimed that he considered the possibility of multiple collisions until 1991. In this year, the huge Yucatan Crater was discovered, which seems large enough to solve the mystery by itself. Kelly and Gurov presented their findings from Ukraine in the August issue of the journal. Science" "Meteoritics & Planetary According to them, the identical birth dates (in geological time terms) of the crater in Ukraine and the Yucatan crater indicate, even if it is not an unequivocal proof, "that together they caused the mass extinction" at the end of the Cretaceous era.
The diameter of the "Bultish" crater is only 25 km, but it is surrounded by a ring of rocky debris that extends over hundreds of square kilometers. This ring evokes in the imagination a combustion of enormous dimensions. The two scientists write in their article that such a collision, if it happened today, would spell disaster for a densely populated country.
Various rock samples from the Boltish Crater have been dated over the years with different dates, from 88 million years to 105 million years. The new dating of the crater by Kelly and Gorov was done with a very precise method, which measures the ratio between two isotopes of the chemical element argon - a colorless and odorless gas that makes up about one percent of the Earth's atmosphere.
Kelly and Gorov report that seven samples of molten rocks from the depths of Baltish Crater yielded an average age of 65.2 million years, with an error range of 600 thousand years. The Chicxulub Crater, on the other hand, has been dated to 65.5 million years, with an error range of 600 thousand years. Given the margin of error, the two collisions that created the craters may have occurred at the same time, or several thousand years apart.
Scientists have recently adopted the idea that comets move in bands. In the 80s, some scientists speculated that showers of comets might have collided with the Earth and thus caused mass species extinctions. The idea gained momentum in 1994 when Comet Shoemaker-Levy 9 broke up and split into 21 pieces, which bombarded the planet Jupiter.
Kelly noted, however, that in his estimation, the chances that the Baltish and Chicxulub craters were created at the same time are not great. However, according to experts, even if it turns out that the times of the collision are close and not the same, it is possible that two blows that occurred one after the other added to the global turmoil that led to the extinction of the dinosaurs and other creatures.
Experts say the new discoveries may provide an answer to an old criticism leveled at the single collision theory. The critics, mainly paleontologists who specialize in the rate of extinction of the dinosaurs, pointed out a long time ago that the fossil finds from the late Cretaceous era indicate a slow decline of many life forms, and not a single and extensive death blow. These findings are inconsistent with the theory of one and only cosmic catastrophe. Now, the emerging connections between the Baltish, Silverpit and Chicxulub craters raise the possibility that a series of collisions contributed to the slow sedimentation of the species.
New York Times
This article was originally published on 5/11/2002 under the title
New Theory on Dinosaurs: Multiple Meteorites Did Them In
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