GILLESPIE LAKE
The rock bed at the Gillespie Lake outcrop on Mars displays potential signs of ancient microbial sedimentary structures similar to those on Earth's ancient rocks. Nasa

A careful study of images taken by Nasa's Curiosity Rover shows structures on Martian rocks similar in shape to those made on Earth by microbes.

The images were taken by the rover as it drove through the dry Gillespie lakebed in Yellowknife Bay.

The shapes include erosional remnants, pockets, domes, roll-ups, pits, chips and cracks, which on Earth can extend from a few centimetres to many kilometres.

Fossilised features in shallow waters and ancient rocks on Earth, known as microbially induced sedimentary structures (MISS), have been studied by Nora Noffke, a geobiologist at Old Dominion University in Virginia for two decades.

In what could be the oldest signs of life on Earth, she had reported finding 3.48 billion year old MISS in Western Australia's Dresser Formation.

These structures are created by colonies of microbes that trap and rearrange sediments in shallow water bodies, which form distinctive features that fossilize over time.

In a paper published in the journal Astrobiology, Noffke points out the striking similarities between Martian sedimentary structures in Gillespie Lake outcrop and those on Earth.

The distribution patterns of the microbial structures on Earth vary depending on the place. Microbial mats that grow in rivers show a different set of associations than those found in seasonally flooded environments, writes Astrobiology magazine.

The patterns found in the Gillespie Lake outcrop are consistent with the microbial structures found in similar environments on Earth.

On Earth these structures change over time. Noffke found that the distribution pattern in Martian rocks corresponds with microbial structures on Earth that have changed over time.

Confirmation of the microbe hand behind the structures can only be had from physically examining the Martian rock samples.

While that could well take a decade or more, the findings add weightage to the recent discovery of organic chemicals in the soil and methane spurts in the Martian atmosphere, indicating microbial life not too long ago.

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