Researchers now believe a cosmic explosion 440 million years ago may have decimated life on Earth.
Kansas University scientists are attracting international attention with their research into the possibility a massive gamma ray explosion caused an ice age that wiped out much of the life on Earth.
"It appears that the (gamma ray) bursts are a serious danger, although not something you would expect to hit us very often, maybe every few hundred million years," said Adrian Melott, a professor of physics and astronomy.
Melott and Bruce Lieberman, an associate professor of geology, are studying whether gamma ray bursts were responsible for high extinction rates in shallow-water marine species -- amoebas, sponges and coral-like creatures and some marine species with hard shells -- while other species survived.
The effects were worse on shallow-water species, the scientists believe, because deeper water protected other species.
"There is a variety of evidence for this particular time period," Lieberman said. "There is chemical evidence as well as the animals that made it through and those that go extinct."
Two international science magazines, New Scientist and Nature, have recently reported the KU researchers' hypothesis.
Others working on the theory since last spring have included Claude Laird, associate professor of physics and astronomy at KU; Mikhail Medvedev, assistant professor of physics and astronomy at KU; and officials from the NASA Goddard Space Flight Center in Greenbelt, Md.
Previous theories have attributed the extinction to the start of an ice age but offer no explanation as to what triggered the ice age during a relatively warm climate.
Gamma-ray bursts occur when a giant star explodes, creating a burst of nuclear energy in the form of gamma-rays, which have the smallest wavelength and most energy of all radiation.
The Earth's atmosphere would absorb the energy, which would separate nitrogen and oxygen molecules in the atmosphere, creating nitrogen oxides, including nitrogen dioxide, which plays a major role in the atmospheric reactions that produce ground-level ozone or smog.
The scientists' research has led them to believe the long-term effects of gamma-ray bursts would deplete the ozone and cause global cooling and acid rain. It would also increase the amount of direct ultraviolet rays from the sun, which only reach a depth of 10 meters in water. This explains why only shallow marine species were involved in the extinction.
The trilobite, an extinct hard-shelled marine creature, has been the focus of research so far. Its extinction pattern in the fossil record is similar to what scientists would expect to find with gamma-ray bursts. They are now looking further into other species that survived and died out during this time to find more connections.
Astronomers have observed and recorded many recent gamma-ray bursts from distant galaxies that have been harmless to the Earth.
"These bursts occurred more often when the solar system first formed," Lieberman said. "Ones like we think caused this extinction occur once every billion years or so, but that's just an estimate."
Melott said if a gamma-ray burst occurred within 10,000 light years on this side of the galaxy, the effects on Earth would be devastating.
"Anyone outside when this occurred would be blinded," Melott said. "The effects would be noticed right away."