A look back in time
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...