Study claims to have discovered the history of life on Earth

A new study has found that the last universal common ancestor (LUCA) appeared on Earth 4.2 billion years ago, meaning life first appeared when the planet was still young.

“We did not expect LUCA to be so old,” says evolutionary biologist Sandra Alvarez Carretero, of the University of Bristol in the UK. “However, our results fit with modern views of the habitability of the early Earth.”

Early Earth was a very different place, with an atmosphere that we would find extremely toxic today. Oxygen, in the quantities needed for life today, did not appear until relatively late in the planet’s evolutionary history (about 3 billion years ago).

But scientists believe that conditions on Earth may have been stable enough to support life about 4.3 billion years ago.

Because our planet is undergoing erosion processes that make it almost impossible to find evidence of that life since that time, the research team, led by evolutionary scientist Edmund Moody of the University of Bristol, studied the genomes of the organisms and the fossil record.

The new study relies on what is called the molecular clock, which is an estimate of the rate of mutations, and counts the number to determine how much time has passed since organisms evolved into forms different from their ancestors.

All living things, from the smallest microbes to the most powerful fungi, have some things in common: they use adenosine triphosphate (ATP) as a source of energy in their cells.

Based on similarities and differences, Modi and his colleagues figured out how long ago the divergent mutations began to appear in the “LUCA successors.” Using sophisticated evolutionary modeling, they were able to learn more about LUCA itself, finding that it was probably very similar to a prokaryote (a single-celled organism that lacks a nucleus).

It was clearly not dependent on oxygen, as there was little oxygen available.

"Our study shows that LUCA was a complex organism, not very different from modern prokaryotes," says Davide Pisani, of the University of Bristol. "But what's really interesting is that it had an early immune system, showing that even 4.2 billion years ago, organisms were arming themselves against viruses."

Since its metabolic processes may produce waste that other life forms could use, it is possible that it appeared shortly after LUCA, meaning that it takes relatively little time for a complete ecosystem to emerge in the evolutionary history of a planet.

“Our work shows how quickly ecosystems could have been established on early Earth,” explains palaeontologist Philip Donoghue, from the University of Bristol. “This suggests that life may have flourished in Earth-like biospheres elsewhere in the universe.”

The study was published in the journal Nature Ecology & Evolution.