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A Very Long Time Ago Indeed

Researchers have timed the presence of the last universal common ancestor to life on Earth to 3.9 billion years ago, earlier than previous calculations, Inverse reports.

A University of Bristol team combined a molecular clock approach with fossil record data to develop this estimate, as the team reports in Nature Ecology and Evolution. They used on 29 universally distributed, protein-coding, mostly ribosomal genes from 102 species to gauge based on differences in those genes how long it has been since they shared a common ancestor.

"We used a relaxed clock framework, which means that the branches across the tree can have differing rates of evolution," first author Holly Betts tells Inverse. She adds that as the molecular clock approach provide relative times, they then relied on "fossil calibrations to anchor the tree in real time."

For instance, they gave the tree of life a hard maximum of 4.52 billion years, which is the planet Theia collided with the Earth to form the moon, an event that sterilized the Earth, as the University of Bristol notes. They also fed in data from fossils, including microfossils from the Strelley Pool Formation in Australia that dates back about 3.4 billion years.

From this, they estimated that the last universal common ancestor to life on Earth arose about 3.9 billion years ago. They also report that this ancestor gave rise to both Eubacteria and Archaebacteria, about a billion years later.