The knobby hills where a Mars rover has spent most of the last four years are dry and desolate. Dust devils occasionally scoot by, and dust storms can almost blot out the Sun.
But billions of years ago, these hills were the Martian equivalent of Yellowstone National Park. Geysers and hot springs dotted the landscape, and steam exploded to the surface, blasting rocks in every direction. The combination of water and heat means the site would have been a comfortable home for life.
At the time, the whole planet was fairly warm and wet. Running water carved riverbeds and filled lakes. Sediments formed thick beds of clay, which still cover much of the Martian surface. It's possible that microscopic life inhabited this wetter environment.
The Columbia Hills are a good place to look for evidence of that life. The Spirit rover climbed into the hills in 2005, and has been poking around them ever since.
A couple of years ago, it uncovered layers of almost pure silica -- a mineral that forms in warm, wet environments, like Yellowstone. Spirit found that several rock formations showed evidence of silica, too. And it found small rocks that were partially embedded in the soil -- as though they'd been blasted into the air and fallen back to the ground.
Spirit doesn't have the right instruments to look for evidence of life. But its observations provide strong evidence that the Columbia Hills were once the Yellowstone of Mars.
Script by Damond Benningfield, Copyright 2009
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