Busy bacteria leave big mark

Earth’s earliest life-forms built mounds on an Antarctic lake bottom

Mats of bacteria here are slowly forming large cone-shaped structures known as stromatolites. They're seen, bathed in blue light, on the floor of an Antarctic lake known as Untersee.

© 2011 Dale T. Andersen http://daleandersen.seti.org

Scientists recently dove into Lake Untersee, a large freshwater lake in Antarctica, and discovered fields of cone-shaped mounds on the lake floor. Though they look like spooky, alien traffic cones, these mounds aren’t the work of extraterrestrials. The scientists say the cones, called stromatolites, were built by bacteria, and the construction project probably took thousands of years.

Under Untersee: A diver collects specimens from stromatolites, cone-shaped mounds built by bacteria, on the floor of Antarctica’s Lake Untersee. © 2011 Dale T. Andersen – http://daleandersen.seti.org
“We had never seen anything like that,” Dale Andersen told Science News. “It totally blew us away.”

Andersen is a researcher at the SETI Institute in Mountain View, Calif. He studies organisms that live in extreme environments, and he braved Lake Untersee’s frigid waters to see the bacteria-built stromatolites and lead a study on them. By studying life in harsh places, scientists like Andersen hope to learn more about life in general.

Over the years, researchers have discovered organisms that can survive in surprising environments not unlike the hostile conditions on other planets. Lake Untersee, for example, is super-cold and contains an abundance of a compound called methane. These same conditions — cold and lots of methane — also describe many of the moons of Jupiter and Saturn.

The View From Above: Beneath the frigid surface of Antarctica’s Lake Untersee are mounds built by ancient bacteria. Wilfried Bauer
Stromatolites are some of the oldest signs of life on our planet. Bacteria started building these structures billions of years ago. Scientists study the fossilized remains of those ancient mounds for clues to how the earliest organisms survived. The underwater discovery in Antarctica gave the researchers a way to peer back in time to the beginning of life on our planet.

“It’s like going back to early Earth,” Dawn Sumner told Science News. Sumner, who also worked on the new study, is a geologist at the University of California, Davis. “These are just incredibly beautiful microbial landscapes,” she says. Bacteria are a type of microbe, or extremely small organism.

Scientists know of only a few places on Earth where stromatolites develop. Andersen and his team say those at the bottom of Lake Untersee have unusual shapes and sizes. The lake’s stromatolites are large: some stand about a foot and a half tall. They’re made mostly of cyanobacteria, which are the earliest known life-form on Earth. Like plants, cyanobacteria convert sunlight to food in the process called photosynthesis.

BRRRRRRRRRRR!
BRRRRRRRRRRR! To reach the surface of the lake, researchers have to cut through a thick layer of ice. Here, Andersen gets ready to go under. © 2011 Dale T. Andersen http://daleandersen.seti.org
The team has explored other lakes in Antarctica but hasn’t found the same stromatolites. Each lake is different: Some have a thicker ice cover, which affects how much sunlight reaches the water and the organisms beneath the surface. The chemical makeup of the water may also vary from lake to lake. So far, the researchers don’t know what makes Lake Untersee a happy home for tall stromatolites.

“There’s something very special about this particular example that’s allowing these large conical stromatolites to form,” Sumner told Science News.

Later this year, the scientists have another chance to investigate: In November, they’ll return to the freezing waters to collect a few more samples of the bacteria-built mounds at the bottom of Lake Untersee. 

Stephen Ornes lives in Nashville, Tenn., and his family has two rabbits, six chickens and a cat. He has written for Science News for Students since 2008 on topics including lightning, feral pigs, big bubbles and space junk.

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