Researchers dress up mass extinction on 'Naked Science'
Because of their unique research into what caused one of the five major mass extinctions, three KU researchers were featured on the National Geographic television series "Naked Science."
The episode, called "Extinctions," aired Nov. 2 on the National Geographic Channel (channel 83 on Sunflower Broadband Cable in Lawrence). It was re-broadcast on Nov. 4.
One of the three biggest mass extinctions of life on Earth occurred about 440 million years ago, at the end of the Ordovician era, when most of the Earth was under water.
Adrian Melott, professor of physics and astronomy; Bruce Lieberman, associate professor of geology; and Mikhail Medvedev, associate professor of physics and astronomy, have teamed up to develop a theory that a gamma-ray burst caused the mass extinction at the end of that period.
Melott describes a gamma-ray burst as "energy released when a very large star, spinning very fast, collapses into a black hole. In this case, you have a big explosion. Instead of being released in all directions, energy goes out in beams."
Those beams traveled 6,000 light years to the Earth, Melott said, in this rare event that happens about every 1 million years in our galaxy.
Lieberman said the explosion delivered a one-two punch to the Earth. It depleted the ozone layer and caused a sudden cooling of the Earth's temperature.
The increased radiation and cooler temperatures increased extinction rates, he said.
Trilobites were among the dominant species on earth during the Ordovician era. These are trilobite fossils from the Yale Peabody Museum of Natural History. Their closest relative today is the horseshoe crab.
Trilobites were among the dominant life forms on the planet at the time. Their closest living relative today would be the horseshoe crab.
"(After) the mass extinction, they come back but not at the same level," Lieberman said. "Eventually there was another extinction and they rebound somewhat. But they never reach the levels of abundance and diversity they had before."
Melott and Medvedev studied the coincidence of mass extinctions occurring when the sun oscillates to the north side of the galaxy.
"At the north end, the solar system is more exposed to cosmic rays, like being exposed to a nuclear reaction," Medvedev said. "That's what causes the extinction."
The cosmic rays cause DNA damage and gene mutations that lead to extinction. It also affects cloud cover, sea level and the Earth's temperature. At the south, the solar system is shielded from those cosmic rays.
Medvedev said this movement occurs about every 63 million years.
The next cycle to the north, and subsequent extinction, is expected in about 10 million to 15 million years.
NASA's astrobiology program funded the group's research at KU with $420,000 in 2004. Melott is the principal investigator on the grant.
He said his team is the primary group investigating the effects of extreme ionizing radiation events, such as the gamma-ray burst, on the Earth and its biosphere.
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