Science Alert reports:

Once upon a time, Earth was barren. Everything changed when, somehow, out of the chemistry available early in our planet’s history, something started squirming – processing available matter to survive, to breed, to thrive.

What that something was, and when it first squirmed, have been burning questions that have puzzled humanity probably for as long as we’ve been able to ask “what am I?”

Now, a new study has found some answers – and life emerged surprisingly early.

By studying the genomes of organisms that are alive today, scientists have determined that the last universal common ancestor (LUCA), the first organism that spawned all the life that exists today on Earth, emerged as early as 4.2 billion years ago.

Earth, for context, is around 4.5 billion years old. That means life first emerged when the planet was still practically a newborn.

“We did not expect LUCA to be so old, within just hundreds of millions of years of Earth formation,” says evolutionary biologist Sandra Álvarez-Carretero of the University of Bristol in the UK. “However, our results fit with modern views on the habitability of early Earth.”

Back when it was new, Earth was a very different place, with an atmosphere that we would find extremely toxic today. Oxygen, in the amount current life seems to need, didn’t emerge until relatively late in the planet’s evolutionary history, only as early as around 3 billion years ago.

But life emerged prior to that; we have fossils of microbes from 3.48 billion years ago. And scientists think that conditions on Earth may have been stable enough to support life from around 4.3 billion years ago.

But our planet is subject to erosional, geological, and organic processes that make evidence of that life, from that time, almost impossible to find.

So, led by phylogeneticist Edmund Moody of the University of Bristol, a team of scientists went looking somewhere else: in genomes from living organisms, and the fossil record. [Continue reading…]