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Antarctic lake microbe structures offer glimpse into life on other worlds

03-14-2012 14:21 BJT

WELLINGTON, March 14 (Xinhua) -- An ancient ice-covered lake in Antarctica is providing scientists not only an indication of the earliest life forms on Earth, but also what life might once have looked like on Mars, a New Zealand researcher said Wednesday.

University of Canterbury limnologist Dr Ian Hawes found unique microbial structures unlike anywhere else on Earth when he took part in an international research expedition in Lake Untersee in the Queen Maud Land area of Antarctica.

Lake Untersee, the largest and deepest freshwater lake in East Antarctica, was extremely unusual, because its crystal clear waters were permanently covered in about 3 meters of ice so there was no contact with the atmosphere, said Hawes in a statement.

Because there were no streams flowing into the lake, it got all its water and gases, including carbon dioxide needed for photosynthesis, from melting ice.

The lake's water, which contained high levels of dissolved methane, was extremely alkaline.

The unusual features had led to the creation of a unique environment as microbial ecosystems in the lake adapted to their unusual surroundings over millions of years, he said.

Hawes' role on the expedition was to study bacterial cone-like structures, known as stromatolites, that cover the bottom of the lake.

"These structures rise up to half a meter from the lake bottom, are covered in a thin layer of intensely purple cyanobacteria ( blue-green algae) and are made up of layer upon layer of organo- sedimentary material. These structures seem to be unique in the modern world yet closely mirror formations that were common in shallow waters around the globe around 2 billion years ago," he said.

"Understanding the functioning of these modern structures can offer insights into how the earliest communities on Earth were organized."

He said cyanobacteria were the oldest lineage of photosynthetic organisms on Earth, having evolved 2 billion to 3 billion years ago, and were thought to have introduced high concentrations of oxygen into the atmosphere and, for hundreds of millions of years in the Precambrian era, they probably dominated the planet.

"The Untersee structures in particular resemble a type of stromatolite known as a 'complex cone,' and these are so far the only known modern example of such stromatolites. There is still controversy over the extent to which this and related kinds of stromatolite are evidence of biology or could be formed by sedimentation alone. The evidence from Lake Untersee comes down on the side of a biological involvement."

He said the astrobiologists were particularly interested in what the lake could tell them about what life could have been like on Mars.

"Mars is extremely cold now, but it used to be a lot warmer and there is a body of opinion that, for a long time, it could have supported Earth-like organisms. Knowing what to look for as incontrovertible evidence of past life is a real challenge, and the communities in Lake Untersee provide more insights into what fossilizable structures are unmistakable evidence of life," said Hawes.

"The structures formed very slowly -- growing at a fraction of a millimeter a year over thousands of years. Slow growth is mainly due to the absence of carbon dioxide in the water, which severely limits photosynthesis, but the very small amount of sediment reaching the lake means that even slow growth can outpace sedimentation.

"Diving beneath the ice of Lake Untersee is an eerie experience. Everything is blue, is super-quiet, the water is crystal clear and spread out before you, and way into the distance are countless numbers of these extraordinary cones. It's easy to imagine that you have dived into a different world."

Hawes would now examine samples collected from the lake.

"As far as we know there are no other ecosystems like this in the world and by studying it we could have a better understanding of what life perhaps used to be like on Earth billions of years ago."

Hawes, also Professor of Antarctic Limnology at New Zealand's Gateway Antarctica and the Waterways Centre for Freshwater Management, worked on the expedition with scientists from the Winogradsky Institute of Microbiology, part of the Russian Academy of Sciences, and planetary scientists from NASA, the SETI Institute in California and the University of California.

Editor:Wang Lingfei |Source: Xinhua

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