Researchers supported by NASA’s Exobiology and Evolutionary Biology program are using modern day microbes to better understand the history of life on Earth. The team is examining stromatolite-building microbial mats in Yellowstone National Park. Stromatolites are found in the geologic record as far back as 3.5 billion years ago, and scientists have long wondered how the structures were formed and what types of organisms built them. The modern-day microbes in Yellowstone may provide the clues they’ve been searching for.