`Elusive Dark Matter May Be Cause for Extinction on Earth'

Dense clumps of elusive dark matter in the galaxy may have caused the worst mass extinction in Earth's history 250 million years ago, a team of Indian physicists says.

Clumps of dark matter passing through Earth would have a direct biological effect and an indirect geological effect, says Afsar Abbas, a professor at the Institute of Physics in India's eastern city of Bhubaneshwar.

"The result would be two waves of extinction, separated by a few million years," says Abbas, lead author of a paper describing this new model for mass extinction in Current Science, a journal published by the Indian Academy of Sciences.

Earth has witnessed several mass extinctions of species over the past 600 million years; the worst of these was the Permian event 250 million years ago that wiped out 90 percent of marine species and 70 percent of life on land. The cause of the Permian mass extinction has been under debate, with previous theories ranging from severe climatic fluctuations to volcanic eruptions to an Earth-asteroid impact.

In the mid-1990s, a Chinese-American team showed that the Permian mass extinction was actually a binary extinction -- an event that involved two pulses of extinction separated by about 5 million years.

"This new model is interesting because it explains the binary event," says the Chinese team-member Xiangning Yang, now a professor at the department of Earth sciences at Nanjing University in China.

Abbas says the dark-matter model predicts two extinction pulses. "The first is caused by the direct interaction of dark-matter particles with living organisms, and the second is caused by long-lasting volcanic eruptions triggered by dark matter at the Earth's core," Abbas says.

From studies of galactic dynamics, astronomers have known for several decades that over 90 percent of the universe is invisible dark matter. Some of this is made up of dead and unborn stars, black holes and planets.

But candidates for dark matter also include weakly interacting massive particles (WIMPS), relics of the Big Bang. The dark-matter model of mass extinction is based on the interaction of WIMPS as Earth passes through dense clumps of these exotic particles.

With the Milky Way enveloped in a dark matter halo, the Earth would always experience a WIMPS wind as the sun moves through the galaxy, but the mass-extinction effect occurs only when the planet encounters highly dense, clumped dark matter.

"The density of particles within clumps is expected to be up to a billion times higher than within the halo," says Abbas.

The first extinction pulse would be the result of mutagenesis, leading to fatal mutations and cancers in living organisms on a global scale caused by interaction of WIMPS with biological tissues, says Abbas.

"This is a nice concept. I'd expect mutagenesis would be the first thing to happen during Earth's interaction with a dark-matter clump," says Konstantin Zioutas, professor of experimental physics at the University of Thessaloniki in Greece. "This hypothesis should motivate experiments to detect biological effects of dark matter," Zioutas told SPACE.com.

Zioutas had been the first to suggest 10 years ago that the interaction of dark-matter particles with nuclei in biological tissues may lead to genetic damage and mutations. He says not just WIMPS but axions -- another candidate particle for dark matter -- may also interact with biological tissues to cause genetic damage.

The secondary, delayed effect of the WIMPS would be intense volcanic activity. During the passage of the clump through Earth, particle annihilation would generate enormous heat at the Earth's core. This heat would gradually rise to the surface and manifest itself as volcanic activity that would lead to the second pulse of extinction of species.

This scenario fits in well with previous theories that associated the Permian mass extinction with volcanic eruptions that lasted up to a million years in what is present-day Siberia. The volcanoes belched out ash, carbon dioxide and sulfur dioxide, precipitating a global cooling -- also previously associated with the mass extinction.

Clumped dark matter may be an additional heat source for planetary bodies and thus may have left calling cards elsewhere in the solar system.

Both extinction pulses would contribute to dramatic reduction in oxygen levels on Earth, a condition called anoxia, known to have been associated with the Permian mass extinction. Paleontologists have suspected that besides the Permian event, the Devonian extinction, which took place around 360-million years ago, was also marked by two pulses, separated by around a few million years.

"The fact that there are double extinction episodes separated by roughly the time it takes for this heat to arrive at the Earth's crust and that the second extinction is correlated with volcanism is a highly enticing signature," says Juan Collar, a physicist at the University of Paris. Collar had first proposed a link between dark matter and extinction four years ago, arguing that the effect of a WIMPS clump on living organisms would roughly be like that of neutron radiation from a close nuclear explosion protracted over the time it took the Earth to cross the clump.

"Satellite experiments are now coming online to look for the characteristic gamma radiation from annihilations in these clumps," says Collar. "If we get evidence for clumpy dark matter halo, the dark matter-induced extinction scenario would be almost inevitable."

"This is a testable prediction of the model -- if clumped dark matter passed through the solar system, there may be relics of heating episodes on planetary bodies," says Abbas.

The enigmatic magnetic field on Ganymede, for instance, points to a molten interior.