Astrobiologists zero in on clues to life

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 was published in Nature. 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, an astrobiologist at NASA Ames Research Center in California's Silicon Valley 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.

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. 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."

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