Wilderness Underfoot: Invasion from outer space?

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If you want to find evidence that extraterrestrials have visited the planet Earth, some scientists think you need only look in the mirror

It’s a long-shot theory at best, but a small number of scientists have been questioning whether all life on Earth might have evolved from microbes that originated somewhere else in the solar system. If true, it would make us aliens.

While not widely accepted, this isn’t necessarily a crackpot idea. The concept is known as “panspermia,” and it simply means that a comet or other body strikes a planet and throws debris imbued with microscopic life into space. The mass travels through the solar system until it lands on another planet. If the new home can support life, the microbes survive. But even as scientists entertain this possibility, they are mostly cautious.

If the Earth was seeded by organisms from somewhere else, they wonder, what is the likely source? Many look to the planet Mars, which has been in the news in recent years with announcements by NASA that ice lurks under the surface in some areas, and that a large ice crater has been found at its north pole. The key ingredient that astrobiologists look for in a planet’s ability to sustain living things is water, whether it’s hot, cold, or frozen. Ice on the red planet means there is now a credible chance that simple life existed there in prehistoric times, and perhaps it is still hidden under the surface today.

Any simple organisms that lived on Mars, whether in ancient or modern times, might resemble “extremophile” microbes found on Earth today. NASA and other scientists are studying these strange earthly organisms to learn more about how life evolves in hostile environments. Sturdy extremophiles can survive boiling in deep sea hydrothermal vents, or freezing in Antarctic ice, or drying out in the hot desert.

But the question of whether Mars or any other planet could support life is the least controversial part of the panspermia theory. Most scientists doubt whether life could survive in a comet or meteor traveling through the extremes of space. They believe the intense heat and cold, and solar radiation, would be too extreme for even the toughest microbes.

From the Oct. 26-Nov. 1, 2005, issue

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