Massive Cloud May Have Frozen the Earth

Like an automobile passing through a dust storm, the Earth’s passage through a giant cloud in space could have led to global freezing that virtually wiped out life on the planet hundreds of millions of years ago.

Two research papers published this year in the journal Geophysical Research Letters outlined a scenario in which the Earth iced over after the solar system passed through a cloud of interstellar dust so large that it took as long as 500,000 years to push all the way through.

Scientists believe the Earth has gone through multiple freezing periods, known as glaciations. Most theories have focused on the idea that large asteroids hit the Earth and kicked up so much dust into the atmosphere that the sun’s rays were blocked, triggering a planetwide freeze.

But the new research looks at two other possibilities. The first proposes a thick cloud of interstellar dust so dense that it screened out the sun. The second scenario, considered more likely, proposes a less dense cloud that stripped away the Earth’s protective ozone layer, allowing harmful cosmic rays to reach the Earth’s surface, poisoning life.

“Computer models show dramatic climate change can be caused by interstellar dust accumulating in Earth’s atmosphere,” said Alexander A. Pavlov of the University of Colorado’s Laboratory for Atmospheric and Space Physics, the lead author of the papers.

According to Pavlov, there is evidence that from 600 million to 800 million years ago there were at least two glaciations that covered much of the Earth, essentially turning it into a huge snowball.

“The big mystery revolves around how they are triggered,” Pavlov said of glaciations.

Pavlov suggested a way to test the new theories: analyze rocks for increased levels of uranium 235, which is not produced on Earth but is present in space clouds.