May 8, 2009 -- It was the first underground movement in our planet's history: Primitive bacteria that lived 2.75 billion years ago built themselves caves to live in, according to a new study. Today, the traces they left behind are stoking hopes that similar life forms could exist on Mars. Early Earth was a rough place to live -- there was no oxygen in the atmosphere, or ozone layer to protect the surface from harmful ultraviolet radiation. Most life at the time protected itself by living in the oceans, or excreting thin films of material that acted as biological shields. The earliest evidence of subterranean life was 1.5 billion years ago, until now. Birger Rasmussen of Curtin University of Technology in Bentley, Australia, and a team of researchers have found what they believe is evidence that bacteria nearly twice as old lived on the roofs of tiny hollows in lake and river sediments. Just a centimeter or so tall and a couple of millimeters across, the 'caves' aren't much to look at. But they formed in a curious fashion -- bacteria grew in air-tight sheets, which inflated like balloons as they trapped methane gas seeping up through the sediments. Related Content:
Methane could have been food for the bacteria, or it could have simply opened space for water to flow through the cavity, carrying sulfur and other nutrients with it. Over time the bacteria built up layer upon layer of material on the cave roofs, descending deeper into the sediment and forming the laminate fossils Rasmussen's team discovered. "Cavity dwelling would've been a good way of escaping harsh radiation at the surface," Rasmussen said. "The cavities were protected and probably had water seeping through." The team's finding, published this month in the journal Geology, strengthens a longstanding hypothesis that similar life forms may be hiding out on Mars. Today the Martian surface is desolate, and probably too harsh to support life -- though much colder, it's similar in many ways to the young Earth. And newly uncovered hints of water provide hope that life underground is still hanging on. "By 2.75 billion years ago, you've got life on land and in the sea, so life in a cave is not that shocking," Robert Rye of the University of Southern California said. "On the other hand, it's nice to know that we have evidence of life in a potentially good analogue environment for underground voids on Mars." Related Links: Discovery Earth for interviews, images and more. Get More NewsSpiders, Scorpions Among World's Oldest CreaturesMany creepy crawlies have been on Earth much longer than previously believed.Blood-Sucking Vampire Bats Sing DuetsWhite-winged vampire bats "harmonize" with separated roost mates.Oldest Hebrew Writing Possibly FoundAncient inscriptions on a 3,000-year-old pottery shard could make history.Rare, Prehistoric-Age Reptile Found in N.Z.A tuatara has been spotted on the New Zealand mainland for the first time in 200 years.Iceman Has No Living RelativesOetzi, the 5,300 year-old frozen mummy, left no living genetic legacy.SLIDE SHOW: Landscapes of TerrorWhat makes a place feel scary? There are scientific explanations.It's Official: People Are Warming the PolesHumans are conclusively to blame for polar warming, say scientists.Eight-Armed Animal Preceded DinosaursWhat may be one of Earth's first animals was no bigger than a coaster and had eight arms.Phoenicians Live on in People's GenesOne in 17 Mediterranean men may be descended from ancient Phoenicians.Pesticides, Fertilizers Linked to Frog DeclineA pesticide is found to promote parasites among amphibians.Hubble Telescope Taking Photos AgainThe Hubble Space Telescope is once again snapping stunning photos of the universe.Andean Mummy Hairs Show Hallucinogen UseScientists find direct evidence of hallucinogenic drug use among ancient Andeans.Opals on Mars Reveal Planet's Long Wet PastOpals found on Mars suggest the planet has been wet for much longer. |
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