The collision of celestial bodies may have prepared the ground for the appearance of the dinosaurs
Tamara Traubman
The greatest extinction of species in history - which occurred about 250 million years ago and which wiped out almost the entire world of flora and fauna - was probably caused by a meteor or a comet that hit the Earth. Similar to the extinction of the dinosaurs, which occurred tens of millions of years later, the collision of the comet or the meteor triggered a chain of events that caused the mass extinction of animals and plants. This is what new evidence published this weekend in the scientific journal Science suggests.
These changes killed about 90% of the species of life in the sea and 70% of the animals that lived on land. In that period, known as the Permian period, lived fish, marine invertebrates, and the first reptiles. The disappearance of the Permians opened the way for the development of the dinosaurs, which appeared in the next period, the Triassic period.
The evidence of the collision was discovered in samples taken from a layer of sedimentary rocks that formed during the extinction. The researchers discovered in those samples gases from an extraterrestrial source that were trapped in football-shaped structures. The spherical structures are made of at least 60 carbon atoms, and are called "bucky spheres" or fullerenes. Helium and argon gases were discovered inside the Buckeye balls. These gases do exist on Earth, but the proportion of isotopes (chemical elements whose weight has changed due to a change in the number of neutrons in the atomic nucleus) is similar to the proportion present in the Sun, and is not at all similar to that on Earth. A few centimeters above and below the geological layer that marks the extinction period, only a very few buckeye balls containing extraterrestrial material have been found.
"I think the relationship between the isotopes of helium and argon is convincing," says Prof. Akiva Bar-Nun, a comet researcher from Tel Aviv University. "It is very difficult to understand how this was created, if its origin is not foreign."
"We think that the Buckeye balls, and the gases inside them, were formed billions of years ago in the outer shell of an ancient star. They moved into interstellar space and were later carried to Earth on a deadly comet or meteor." This is what the head of the research team, Dr. Luan Becker from the University of Washington, said. According to her, the comet or meteor may have triggered a chain of events, including massive volcanic eruptions, changes in sea level and extreme climate changes.
Until recently, many scientists believed that the Permian extinction took place over a very long period of time, about 10 million years. Therefore, the accepted explanation was that gradual climate changes caused the extinction. However, new research suggests that the extinction may have occurred in a period of only 8,000 to 100 years.
The findings raise a new puzzle. During the extinction in the Permian period, a massive volcanic eruption occurred in Siberia, which released quantities of lava sufficient to cover the earth in a layer of three meters. Collisions of large objects on Earth and volcanic eruptions on the scale of the eruption that occurred in Siberia are extremely rare and only occur once every tens of millions of years.
"It's hard to believe that this is just a coincidence," says Prof. Bar-Nun. "It is possible that the tremendous volcanic activity resulted from the impact of a giant meteor or comet that dug a hole deep enough for large amounts of lava to emerge from the Earth's liquid mantle", similar to the giant craters on the moon.
Becker and her colleagues previously discovered Buckeye balls in a crater in Canada, and in two meteorites. They also found buckeye balls containing similar ratios of gases in a layer of sediment from the time when the dinosaurs went extinct.
The Baki balls in the current study were found in rock samples from Japan and China. The researchers also sampled sedimentary rocks in Hungary, but almost no Buckeye balls were found there. Scientists who did not participate in the study said that samples from other areas would be necessary to confirm the findings.
{Appeared in Haaretz newspaper, 25/2/2001{
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