Far from being a miracle that happened just once in 4 billion years, life's beginnings could have been so commonplace that it began many times over

Graham Carter

IN 4.5 billion years of Earthly history, life as we know it arose just once. Every living thing on our planet shares the same chemistry, and can be traced back to “LUCA”, the last universal common ancestor. So we assume that life must have been really hard to get going, only arising when a nigh-on-impossible set of circumstances combine.

Or was it? Simple experiments by biologists aiming to recreate life’s earliest moments are challenging that assumption. Life, it seems, is a matter of basic chemistry – no magic required, no rare ingredients, no bolt from the blue.

And that suggests an even more intriguing possibility. Rather than springing into existence just once in some chemically blessed primordial pond, life may have had many origins. It could have got going over and over again in many different forms for hundreds of thousands of years, only becoming what we see today when everything else was wiped out it in Earth’s first ever mass extinction. In its earliest days on the planet, life as we know it might not have been alone.

And what about life on other planets? Read about the search for life in the solar system’s other seas

Just to be clear, what we are talking about came long before animals or plants or even microbes. We are going right back to the start, when the only things fitting the description of “life” were little more than molecular machines. Even then, having stripped away bodies, organs and cells and reduced everything down to the essential reactions, things appear devilishly complex. At a bare minimum, life needs some kind of …