Ancient Antarctic Lake Reveals How Life Got a Foothold on Earth (Today’s Most Popular)

 

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An Antarctic discovery in April of 2011 could  help scientists better understand the conditions under which the planet's primitive life-forms thrived. “It’s like going back to early Earth,” says Dawn Sumner, a geobiologist at the University of California, Davis, describing her explorations of the eerie depths of East Antarctica’s Lake Untersee where Sumner and her colleagues, led by Dale Andersen of the SETI Institute in Mountain View, Calif., discovered otherworldly mounds of Photosynthetic microbial stromatolites.


The stromatolites, built layer by layer by bacteria on the lake bottom, resemble similar structures that first appeared billions of years ago and remain in fossil form as one of the oldest widespread records of ancient life dating from 3 billion years ago or more, to understand how life got a foothold on Earth.

Lake Untersee is located at 71°20'S, 13°45'E in the Otto-von-Gruber-Gebirge (Gruber Mountains) of central Dronning Maud Land. [Download Google Earth .kmz file of Lake Untersee]. The lake is 563 meters above sea level, with an area of 11.4 square kilometers and is the largest surface lake in East Antarctica.

The purple-bluish mounds are composed of long, stringy cyanobacteria, ancient photosynthetic organisms. Similar to coral reef organisms, the bacteria takes decades to build each layer in Untersee’s icy waters, Sumner said, so the mounds may have taken thousands of years to accumulate.

Today, stromatolites are found in only a few spots in the ocean, including off the western coast of Australia and in the Bahamas. They they have also been found thriving in freshwater environments, such as super-salty lakes high in the Andes and in a few of Antarctica’s other freshwater lakes.

But scientists the size and shape of the purplish stromatolite mounds built by Phormidium bacteria in Untersee's extremely alkaline waters and high concentrations of dissolved methane, are unique reaching up to half a meter high, dotting the  lake floor. “It totally blew us away,” Andersen said. “We had never seen anything like that.”

The stromatolite mounds were found adjacent to smaller, pinnacle-shaped lumps made of another bacterial group, Leptolyngbya.

“Everywhere else that we’ve looked you have a gradation between the structures,” like in bacterial mats sprawling around Yellowstone’s hot springs, she said. “There’s something very special about this particular example that’s allowing these large conical stromatolites to form.”

Andersen’s team has also studied Lake Vanda, which has a more transparent ice cover that lets more light penetrate, and Lake Joyce, with its thicker ice, which constrains how far down photosynthesizing organisms can grow, without finding large conical stromatolites there.

The Daily Galaxy via astrobiology.com

Image Credit: Dale Andersen

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