Beneath nearly 20 meters of solid Antarctic ice lies a salty lake that has been sealed off from the atmosphere for close to 3,000 years. According to a report published online this week by the Proceedings of the National Academy of Sciences Lake Vida contains the thickest nonglacial lake ice cover on earth, which houses centuries-old bacteria. The findings could help researchers in their hunt for evidence of life in other extreme environments, such as Mars.

Lake Vida is located in the McMurdo Dry Valleys region of Antarctica, and its surface remains frozen year round. In fact, scientists thought that it was one of several lakes that are completely frozen to their beds all year long. But Peter T. Doran of the University of Illinois and his colleagues determined that ice cover conceals water that is salty enough to remain liquid at temperatures below -10 degrees Celsius. Sediments locked within the ice core a few meters above the water-ice boundary date to 2,800 years ago, the team determined. What is more, bacteria found in the dirt revived once they were liberated from the ice and exposed to water. "The ice covers of these lakes represent an oasis for life in an environment previously thought to be inhospitable," says study co-author John Priscu of Montana State University. "These life forms may possess novel ice-active substances such as antifreezes and ice nucleation inhibitors that allow the organisms to survive the freeze-thaw cycles and come back to life when exposed to liquid water."

Indeed, the frigid temperatures proved perfect for preserving the DNA of the ancient organisms. By studying them, the scientists hope to gain a better understanding of how life might have evolved in other regions of Antarctica such as Lake Vostok, which sits under four kilometers of the East Antarctic ice sheet. The icy lake could also inform potential scenarios for life on a young Mars. "While we don't expect to find 'Lake Vidas' on Mars today, it's a good analogue for something in Mars's past," says Doran. "Mars is believed to have a water rich past, and if life developed, a Lake Vida-type ecosystem may have been the final niche for life on Mars before the water bodies froze solid."