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MrPlow writes:

Submitted via IRC for takyon

According to a paper released Monday in Nature Ecology & Evolution, the still-unidentified microbe that scientists believe is the ancestor to all cellular life on Earth was born sometime before 3.9 billion years ago. As it turns out, the last universal common ancestor — LUCA for short — emerged even earlier than scientists once believed.

Scientists previously pegged the LUCA's birth to a period 3.5 to 3.8 billion years ago, but the new evidence examined in the study⁰ suggests it happened one hundred million years earlier. The researchers from the Universities of Bristol and Bath determined the LUCA's new age using the concept of the "molecular clock," which does away with all of the issues with relying on fossils to build Earth's early-life timeline. With early life fossils, there are always older ones waiting to be exposed, which may seem exciting but makes creating an early-life timeline very difficult. The molecular clock, in contrast, uses differences in the genomes of individual species to tell how much time has passed since they shared a common ancestor. The basic idea is that the more mutations two species share, the more time has passed since their evolutionary paths diverged.

The team applied a variant of this approach to some of the oldest existing fossils ever found, hoping they'd reveal when LUCA was born. "We used a relaxed clock framework, which means that the branches across the [evolutionary] tree can have differing rates of evolution," explains first author and University of Bristol Ph.D. candidate Holly Betts to Inverse. Because the differences in age that the molecular clock technique gives are relative, she explains, "you then use fossil calibrations to anchor the tree in real time."

Source: https://www.inverse.com/article/48247-early-life-domain-molecular-clock

⁰DOI: 10.1038/s41559-018-0644-x

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