Say what you will about the simple, uninteresting lives of microorganisms, they’re tough little critters. You try surviving for a million and a half years without heat, food or sunlight and see how you do. A team of National Science Foundation researchers just discovered a species of Antarctic organisms that has accomplished exactly that — and the microbes’ unlikely survival can tell us a lot not just about the adaptability of life on Earth, but the prospects for it on Mars.
The fact that organisms can survive in extreme — seemingly lethal — conditions is nothing new. Researchers have found creatures living at boiling vents on the floor of the ocean, in desert sands that virtually never see water; fossilized remains of microorganisms have even been found inside of rocks. Antarctic life, however, has always been a more complex matter. Antarctica was once a warmer, wetter land than it is now, but continental migration pushed it from place to place, leaving it — for the current epoch at least — at the bottom of the planet, where it became little more than a frozen desert. Its valleys are some of the driest places on the Earth, receiving less than 4 inches of precipitation per year. Species that thrived when Antarctica was green would have been entirely wiped out, unless they could adapt — and fast.
A team led by microbiologist Jill Mikucki of Dartmouth College, set out to look for any such hangers-on at a particularly unforgiving place: Blood Falls, on the East Antarctic Ice Sheet. Blood Falls got its unlovely name due to red staining that comes from a snout on the Taylor Glacier — the result of heavy deposits of iron in its water. In ages past, a fjord ran through the area and brought with it swarms of marine life, but more than 1.5 million years ago the ice began to rise, and a pool of seawater became trapped — and then capped — creating a huge, salty deposit buried hundreds of yards beneath the glaciers.
Mikucki and her group began sampling water that runs from deep within the glacier — which warms just enough in the Antarctic summer that it melts. Freed up after 1,500 millennia of absolute blackness and utter cold, the water at first seemed completely sterile. “When I started running chemical analysis on it,” says Mikucki, “there was no oxygen.”
What there was, however, was life. The samples Mikucki collected did not teem with a riot of different microbial species the way ocean water does, but there was at least one species, thriving and dividing and doing all of the other things single-celled species do. “How [were] they able to persist below hundreds of meters of ice and live in permanently cold and dark conditions over hundreds of millions of years” Mickucki asks
The trick, she found, was that they learned how to change their diet. When Mikucki studied the organisms’ DNA and energy-processing systems, she found that they were indeed descended from species that once lived in the open ocean. Underneath the ice, they were deprived of light to run photosynthesis, and instead they relied on what they found around them — principally sulfur and iron — to generate energy. The genes responsible for that alternative metabolism are also found in other marine organisms but they’re less important to those species because the oceans provide more options for food.
Mikucki refers to the subglacial pond as “a unique sort of time capsule from a period in Earth’s history,” but it also has lessons for scientists studying Mars, an entire planet that is in many ways a time capsule too. Mars, like Antarctica, was once warm and wet, but the slow loss of its atmosphere also meant the loss of much of its moisture and surface heat. Still, the place was warm and wet long enough for life to have taken hold — life that would have then had to retreat into underground water deposits and make the same kind of hurry-up adaptation Mikucki’s microbes did. Similar adaptive metabolism could be in evidence on the Jovian moon Europa, where a layer of surface ice may cover a globe-girdling ocean.
It’s entirely possible that we’ll never find any proof that life exists anywhere else in our limited little solar system. But courtesy of our own Antarctic, we now have one more piece of proof that it could.
