Looking for life, Astrobiologists Dive Deep

Coral-like mounds on the floor of a Canadian lake may
make it easier someday to identify life on other planets.

A team of interdisciplinary astrobiologists from NASA and
other agencies is homing in on recognizing the microbial
biosignatures for life, making it easier someday to identify
life on other planets.

A scientific paper analyzing the team’s research results,
titled “Modern Freshwater Microbialite Analogues for
Ancient Dendritic Reef Structures,” was published in the
journal Nature on October 5. The paper focuses on the
study of mounded microbialite deposits – layers of living
and non-living organisms – found at Pavilion Lake in
Canada.

Microbialites are organic sedimentary mineral deposits
covered by a thin layer of microbes that become entombed
in the mounds as they grow outward.

“These unique and rare microbialite formations are
important to NASA’s astrobiology effort because they are
big, macroscopic evidence of microscopic life,” said Dr.
Chris McKay, a scientist with the NASA Astrobiology
Institute and one of the paper’s authors. “They are helping
us understand one of the big astrobiology questions – how
early life took hold and began to flourish on Earth. These
fossils are like seeing a billion-year-old footprint in the
sand and comparing it to a modern human foot,” he said.

NASA scientists and others began studying the mounded
deposits growing in Pavilion Lake, British Columbia,
Canada, in 1998. The microbialites were formed layer by
layer with the oldest on the bottom. This structure provides
a record of growth and yields important clues about the
organisms that once lived there.

The odd-looking mound formations, discovered by
recreational divers in 1997, are unique, scientists say, and
differ from the Earth’s oldest known structures called
stromatolites, 3.5-billion-year-old formations in Western
Australia, which show no direct evidence of life.

The microscopic organisms at Pavilion Lake created large
visible structures that scientists need to explore further,
according to McKay. The mounded structures are
relatively young in geological terms, he added, being only
about 12,000 years old.

“At spring-fed Pavilion Lake, we studied the rock textures
in the mounds that reflect the different roles played by the
living microbes who created the microbialites versus the
natural environmental mineral precipitation activity there,”
said Dr. Sherry L. Cady, assistant professor of geology at
Portland State University and editor of the journal
Astrobiology. “It’s a unique natural laboratory,” she said.
Cady analyzed the microbialites using electron microscopy
to determine if the mounds were of organic (biological) or
inorganic origin. “Teasing out which components of the
mounds were biological is key,” Cady said.

According to McKay, the first to dive and view the
mounds, they are especially interesting to astrobiologists
because their shape changes as the lake gets deeper. “The
stuff on top was soft like cauliflower, while the stuff on the
bottom was hard like artichokes. I had never seen anything
like this before in the world, especially in a freshwater
lake,” he said.

What Next?

Research is still ongoing about the different types and
textures of mounds that formed in different parts of the
lake, he added. The research is also important because
scientists may find similar structures on Mars, McKay said.
“One goal of this work is to help us better understand and
recognize carbon-based microbial biosignatures for life on
Mars.” This research will help target future Mars landing
sites where life is most likely to be found and help
researchers fine-tune tools for Mars sample return
missions, he said.

“When we walk on Mars, it’ll be hard to spot a
microscopic-sized fossil. But if we see stromatolities or
microbialites, we can send a rover there, and it may turn
out to be a marker for Mars life.” Pavilion Lake is located
in a box canyon, similar to some of the canyon features on
Mars, according to McKay. Scientists say future research
at the site will include a winter dive under the ice and
studying the formations for a full year, under seasonal
conditions.