A new study claims we have found some answers to some of the tough questions we’ve been asking ourselves since we first became self-aware and curious about who we are and where we came from. The results suggest that life begins surprisingly early.

Origin of life

By studying the genomes of present-day organisms, scientists have determined that the universal common ancestor (LUCA) that gave rise to all subsequent life currently existing on Earth arose very early. 4.2 billion years ago.

For context, the Earth is about 4.5 billion years old, meaning that life first appeared when the planet was still young.

We did not expect LUCA to be so old, only hundreds of millions of years after the Earth formed, but our results are consistent with current views on the habitability of the early Earth.
– says evolutionary biologist Sandra Alvarez-Carretero of the University of Bristol in Great Britain.

If we could go back in time and look at Earth at that time, we would barely recognize it. The atmosphere was now toxic to life, and everywhere you looked there were only rocks and stones, no plants or animals. The amount of oxygen needed for modern life only appeared relatively late in the planet’s evolutionary history, about 3 billion years ago.

But life emerged even before that. We have fossil microbes 3.48 billion yearsBut scientists have suspected for some time that conditions on Earth may have become stable enough to support life around 4.3 billion years ago.

Unfortunately or fortunately, our planet is subject to erosion, geological, tectonic and organic processes that make the probability of finding evidence of life at that time almost zero.

Methodology

So a team of scientists led by phylogeneticist Edmund Moody of the University of Bristol began looking elsewhere: in the genomes of living organisms and fossil remains.

Their research is supposedly based on: molecular clockIn fact, we can estimate the rate at which mutations occur and, by counting their numbers, determine how long it took for the organisms in question to diverge from their common ancestor.

All organisms, from the simplest microbe to the most powerful fungus, have one thing in common: they share a universal genetic code. The way we produce protein is the same. There is a nearly universal sequence of 20 amino acids oriented in the same direction since the beginning of time. And all living organisms use adenosine triphosphate (ATP) as an energy source in their cells.

Based on these similarities and differences, Moody and his colleagues calculated how much time had passed since LUCA’s successors began to diverge from one another. Using sophisticated evolutionary modeling, they were able to learn more about the LUCA bacteria, what it was like, and how it survived on Earth, which was so inhospitable to its distant descendants.

How did he do this?

• The scientists discovered that LUCA is very similar to prokaryotes, which are single-celled organisms that lack a nucleus and membrane-bound organelles, unlike more complex eukaryotes.
• It was clear that it was not dependent on oxygen, which is no surprise to this microbe, as there was very little oxygen in the atmosphere at the time.
• LUCA metabolic processes likely produced acetate.

But there’s something even more interesting. It turns out LUCA wasn’t alone in the newborn world.

“Our work showed that LUCA was a complex organism, not very different from modern prokaryotes. But what was really interesting was that it had an early immune system. This means that 4.2 billion years ago, our ancestors were engaged in an arms race with viruses.”
– says phylogenist Davide Pisani from the University of Bristol.

These may have appeared soon after LUCA’s emergence, as LUCA’s metabolic processes produce waste products that other life forms can use.

This means that It takes relatively little time in the evolutionary history of the planet for a full-fledged ecosystem to emerge. Moreover, we understand that life is quite successful in Earth-like biospheres elsewhere in the universe.