Earth Institute News
Miles Below Antarctic Ice,
a Freshwater Lake May Harbor Ancient Life
By Robert Lee Hotz, L.A. Times Science Writer
Part 3: They're Everywhere
VOSTOK, ANTARCTICA--Microbes can be found in rocks a mile underground and in the clouds overhead. Some microbes make their home in toxic waste, while others shrug off radiation or survive in brine five times saltier than the sea. Many species of single-celled creatures readily grow in the absence of oxygen, warmth and light.
And, if one recent published research report can be believed, at least one spore-forming microbe survived unthinkable extremes of time, reviving after being dormant for 250 million years.
So many simple organisms thrive in conditions lethal to conventional life forms that biologists now suspect that life must have evolved under conditions dramatically different from those so hospitable to humankind today.
The first single-celled citizens of Earth may have taken form during a primordial time of fire and ice about 750 million years ago when the entire planet looked something like Lake Vostok, some biologists speculate.
They envision a primitive "snowball Earth" encrusted in a rind of ice that covered pockets of water kept liquid by the heat from geothermal vents. There, protected from space by the ice and invigorated by the energy of the hot vents, microbes adapted and evolved in an intricate dance with extremes of heat and cold.
Today some heat-loving microbes thrive in temperatures above the boiling point of water in hot springs and deep-sea volcanic vents. A few microbial species find temperatures less than 194 degrees Fahrenheit too cold to reproduce.
At the other extreme, bacteria living in the sea ice around Antarctica find it too hot to breed if the temperature gets much above 53 degrees. Bacteria discovered in the gravel under alpine glaciers in Switzerland live quite comfortably at the freezing point of water.
In the interior of Antarctica, with winds so violent and ice so thick that no root can hold, life ekes out a surprisingly rich existence.
Some microbes find refuge from the cold between the grains of porous stone.
Others live and die in the minute gaps between snow crystals at the South Pole, biologist Ed Carpenter at San Francisco State University and USC environmental biologist Douglas Capone discovered.
Those one-celled organisms were comfortable living in prolonged darkness and at temperatures so low that liquid water normally a prerequisite for life on Earth is almost completely absent.
The ambient temperature in the snow where they were found hovered just above 1 degree Fahrenheit. Their habitat was continually bathed in high levels of sterilizing ultraviolet radiation common in the polar region.
To survive in such conditions, these seemingly simple creatures each inherit four copies of their genome and an elaborate DNA repair mechanism that compensates for the destructive genetic effects of radiation and desiccation.
In ice samples taken a few hundred feet above Lake Vostok at a depth of 11,778 feet below the surface--scientists recently discovered dormant colonies of microbes.
At that depth, the ice itself turns from cloudy, tightly packed crystals to larger, almost transparent "gem" ice. Researchers believe that is a sign that the ice is composed not of ancient compacted snow but of frozen water from the lake itself.
Using DNA fingerprinting techniques, ecologist Priscu and his colleagues determined that these bacteria are closely related to species of soil microbes found elsewhere in Antarctica. So far, no one knows whether these bacteria actually lived in the lake and evolved there, or sifted down through the ice from the surface over half a million years.
If microbes do survive in the lake, they are micro-denizens of perpetual darkness with no obvious source of food and under a weight of ice so heavy that the water in which they swim contains almost no dissolved oxygen, methane or other gases.
"The more we look, the more we see that life can adapt to more extreme conditions than we ever imagined," Carpenter said. "It makes microbial life on other planets seem a little more plausible."
Copyright 2001 Los Angeles Times
Reprinted with Permission