How Life Began

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Finally, there's a cosmic dimension to these bugs. So-called exobiologists and astrobiologists, who speculate about life beyond Earth, have long assumed that liquid water is a minimum requirement for existence. But if that water can range from frigid to boiling, and if burial underground isn't a problem, then it's not crazy to think that life exists in the permafrost beneath the surface of Mars, or in the ice-capped ocean that may encircle Jupiter's moon Europa, or in the seas that may exist on Saturn's moon Titan. Indeed, NASA considers extremophiles so relevant to its search for life in the universe that in 1997 it created the Astrobiology Institute at its Ames Research Center near San Francisco, devoted in part to the study of these peculiar organisms.

The idea that America's space agency would one day focus on extreme microbes would have seemed utterly farfetched in the late 1960s, when researchers discovered a microbe known as Thermus aquaticus in near boiling springs in Yellowstone National Park. At the time, the bizarre creature seemed little more than a biological oddity.

But a decade later, deep-diving submersibles scanning the midocean ridge near the Galapagos Islands stumbled on something totally unexpected: plumes of toxic water spewing from cracks in the sea floor. Huddled around these awful oases were entire ecosystems made up of hundreds of hitherto unknown species, ranging from bright red tube worms to ghost-white crabs and anemones.

At the bottom of the food chain were microbes that, scientists soon realized, were thriving on nothing more than heat and poison. "They make a living," explains John Baross, of the University of Washington's School of Oceanography, "by oxidizing sulfide, methane, iron and other metals." After years of digging into the sediments in and around vents, Baross discovered that these microbes have adapted to a wide variety of thermal conditions, from room temperature to well above boiling.

While their hardiness was a big surprise, the microbes' ability to eat hydrogen, sulfur, manganese and other chemicals--a process known as known as chemoautotrophy--was a revelation. Until then, all living systems were thought to depend on photosynthesis, using sunlight as a primary energy source. (Even cave-dwelling or deep-water creatures who never see the sun eat organic matter that ultimately originates from photosynthesis.) But if life could thrive without even indirect contact with sunlight, the amount of potentially habitable real estate on the planet would expand considerably.

And indeed, life began to turn up just about everywhere scientists looked. Geologists had been arguing since the 1920s, in fact, that chemical contaminants found in crude oil suggested that some sort of life was thriving underground. They weren't taken seriously until the 1980s, though, when Department of Energy scientists realized that if subsurface microbes really did exist, they might play a key role in regulating the purity of groundwater. So they began digging boreholes at DOE sites in South Carolina and Washington State.