July 23, 2008

Fossil Discoveries Date Dry Valley’s Mars-Like Origin

A range of fossils found in sediments on the slopes of Mount Boreas have helped refine the timing of the climate shift that gave rise to Antarctica's remarkable Dry Valleys.

The famously ice-free terrain enjoyed more benign, tundra-like conditions 14 million years ago - but then flipped to the intensely cold setting seen today.

Ancient lake-living shrimp-like creatures can pinpoint the big switch, scientists say.  They believe the ostracods would not have coped with a harsh, dry environment.

"Our dating says the lake existed 14 million years ago, and within about 250,000 years of that lake existing and holding those ostracods, all the glaciers in the surrounding area stopped melting and they become cold-based and began to evaporate," said Dr. Adam Lewis, from North Dakota State University.

"So after about 13.8 million years ago, there's no water"”it's bone dry, dry-frozen," he added.

The Dry Valleys in Antarctica, with their barren gravel-strewn floors, are said to be the closest place on Earth to Mars.

There is so little precipitation in the valleys that they are technically regarded as deserts since the air that falls into the region from the continent's elevated interior has extremely low humidity.

Seals and other animals that wander into this landscape and get lost will die and mummify.

The fossils found on the edge of McKelvey Valley, include mosses, diatoms and beetles. But it is the 1mm-long ostracods that are the most special"”each are exquisitely well preserved, with their soft tissues visible in three dimensions.

"We've got the legs and the mouth parts, and the reproductive organs; and we can even see micron-scale hairs on the legs," said Dr. Mark Williams, from the University of Leicester, UK.

"This is a first of its kind from the Antarctic; it's unusual in the fossil record in general.

"Notwithstanding the significance of the fossil preservation, the presence of lake ostracods at this latitude, 77 degrees South, is also of great note. With modern ostracod distribution, the most southerly ones are at about 60 degrees South."

The fossils represent a precise marker, indicating the switch from conditions which one might see in Northern Canada and Iceland today, where summer warmth brings a melt, liquid water and a flourish of life - to the more severe, arid conditions we recognize in the Antarctic today.

"This also helps us understand the whole evolution of Earth's climate system because you've got this huge climate jump that takes place about 14 million years ago when the oceans reorganize, Antarctica freezes over - a whole host of things change right at that point," said Williams.

"What we're doing with these ostracods is to say: 'that's it, that's the point'," he added.

The fossil research is further detailed in the journal Proceedings of the Royal Society B.


On the Net: