How Life Began
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GBF/SPL/PHOTO RESEARCHERS
ICE LOVERS: These microbes multiply in Antarctic lakes |
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It's hard to imagine a more inhospitable place on earth than the hydrothermal vents that pepper the ocean floor. These cracks in the sea bottom spew water superheated by rising magma to as high as 750 degrees F and contaminated with toxic substances such as hydrogen sulfide, cadmium, arsenic and lead. Yet despite these lethal conditions, life not only survives but thrives in the form of colonies of microbes that feed on poison and multiply in temperatures that could hard-boil an egg.
The frozen continent of Antarctica is almost equally deadly, but at the other end of the temperature scale. Drill into the ice cap a mile, then another, and you reach, improbably, a body of water known as Lake Vostok that rivals Lake Ontario in size. While scientists haven't yet drilled into the lake itself, they have pulled up samples of frozen lake water clinging to the bottom of the ice cap that contain unmistakable evidence of microbial DNA. Although it hovers near the freezing point, cut off from light and outside nutrients, Lake Vostok is teeming with microorganisms. "Nobody," marvels John Priscu, a Montana State University microbiologist who has studied the samples, "thought there could be any life down there."
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Remarkable as these discoveries might once have seemed, they have become almost commonplace. In the past few months alone, researchers have extracted colonies of microbes that thrive at 137 degrees F in an underground hot spring in Idaho and found others eating into volcanic rock 1,200 ft. beneath the sea floor. Over the past few years, in fact, scientists have been finding life in all sorts of places where biology textbooks say it shouldn't exist. Microorganisms are thriving in thermal springs in Yellowstone National Park and in pristine veins of water two miles underground in South Africa. They're living in solid rock at the bottom of deep mines. They're growing in brine pools five times saltier than the ocean, in tiny pockets of liquid embedded in sea ice and in places with toxic levels of heavy metals, acids and even radiation.
Taken one at a time, these creatures — formally known as "extremophiles," or lovers of extreme environments — are fascinating curiosities. Collectively, they have triggered a scientific revolution, forcing researchers to rethink biology's most basic assumptions about how life began.
Extremophiles also represent a biotech bonanza, pumping out unique substances that could be invaluable in all sorts of industrial and medical applications (see box). Polymerase chain reaction (PCR), for example, the DNA-amplifying method used most famously in the O.J. Simpson murder trial, exploits an enzyme manufactured by a Yellowstone extremophile.
But the importance of these microbes goes much further. While some extremophiles are bacteria, some are so different from any other single-celled organism that scientists have created a new biological kingdom, called Archaea (from archaic), to accommodate them. As the name suggests, Archaea may be similar to the very first organisms that populated the earth billions of years ago. The implication: life on our planet may first have arisen, not in a warm tidal pool as Darwin and others theorized, but under conditions of sulfurous, searing heat.
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.
Tom Friedman
August 30 - September 5, 2008
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