The earliest fossils of microbes themselves, rather than just their by-products, preserve the remains of what scientists think are sulfur-metabolizing bacteria. The fossils also come from Australia and date to about 3.43.43, point, 4 billion years ago^2
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Bacteria are relatively complex, suggesting that life probably began a good deal earlier than 3.53.53, point, 5 billion years ago. However, the lack of earlier fossil evidence makes pinpointing the time of life’s origin difficult (if not impossible).