The ring would have taken about a hundred thousand years to form, says University of New Mexico climatologist Peter Fawcett. Eventually, after 2 million or 3 million years, as the orbiting debris fell to Earth and burned up in the atmosphere, the ring would have disappeared. While it lasted, says Fawcett, it would have wreaked havoc with climate--and with whatever life survived the impact. Fawcett and Mark Boslough, a physicist at Sandia National Laboratories, made computer simulations that showed the ring would have cast a deep shadow on the ground, much like a total solar eclipse. The size and location of the shadow would have varied with the seasons.
The biggest shadow, more than 650 miles wide, would have fallen in the Northern Hemisphere on December 21, darkening a swath across Mexico, the Caribbean, and the Sahara Desert; on June 21 the Southern Hemisphere would have been under maximum shadow.
"The shadow would have turned warm tropical rain forests into colder, temperate regions--and that would have put a huge amount of stress on life," Fawcett says. "Life would have had to adapt--and then adapt again when the ring went away."
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