When Bacteria Began: Decoding the Past with Ancient Alliances

Understanding when bacteria first emerged on Earth is a big puzzle, mainly because bacteria fossils are rare. Scientists have found a new way to solve this puzzle by looking at ancient partnerships between bacteria and other life forms. They used genes found in mitochondria–the tiny powerhouses inside our cells that were once bacteria–to create a family tree of bacteria. This tree helps connect the dots from the evolution of more complex life forms like animals and plants, which have more fossil records, back to their bacterial ancestors.

The scientists created a new mathematical method to handle uncertainties in this tree. They applied 19 rules that helped them estimate when different bacteria first appeared. They also developed a tool to handle changes in DNA that happen over long periods, making the timeline more accurate. Their findings suggest that all bacteria we know today evolved from a common ancestor around 4. 0-3. 5 billion years ago. After this common ancestor, bacteria quickly branched off into different groups. This timeline can help scientists study how bacteria diversified and how these changes relate to major events in Earth's history.

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