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Bacterial Growths May Offer Clues About Earth's Past

By linking the odd geometry of bacterial growths to photosynthesis, researchers may have a new way to study Earth’s oldest fossils.

About 85 percent of the history of life on Earth has been solely microbial, meaning that single-celled organisms ruled the planet for billions of years before more complex life evolved. One way that geologists try to decipher how these cells functioned as far back as 3 billion years is by studying modern microbial mats, or gooey layers of nutrient-exchanging bacteria that grow mostly on moist surfaces.

These layers collect dirt and minerals that crystallize over time. Eventually, the bacteria turn to stone just beneath the crystallized material, thereby recording their history within the crystalline skeletons. Known as stromatolites, the layered rock formations are considered to be the oldest fossils on Earth. While there are many kinds of stromatolites, many geologists believe that the odd triangular patterns of conical stromatolites are the purest record of bacterial growth because they form as a result of only two processes: the growth of bacteria and the growth of mineral crystals.

Deciphering the few clues about ancient bacterial life that are seen in these poorly preserved rocks has been difficult, but researchers from MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS) and the Russian Academy of Sciences may have found a way to glean new information from the fossils. Specifically, they have linked the even spacing between the thousands of tiny cones that dot the surfaces of stromatolite-forming microbial mats — a pattern that also appears in cross-sectional slices of stromatolites that are 2.8 billion years old — to photosynthesis. The connection could help scientists put a better range on when photosynthesis started.
 
 

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