The dating of the oldest living beings on Earth is giving more lurches than expected. In the two thousand years we gave the date of 3.9 billion years ago, which was truly remarkable, since the Earth was formed 4,500 million years ago, so that the first bacteria would have originated only 600 million years later; and those 600 million years were a hellish period of impacts of huge meteorites -one of them took the moon from us- and other geological imponderables. These hurries were alleviated shortly after, when the fossils of 3.900 million years lost their credibility: in fact they were formed by common geological processes, without biological contribution. A deception of the stones. The most credible date for the first fossils came to 3,450 million years ago (almost a billion years after the formation of Earth).
And so we continued until 2016, when the melting of Greenland allowed a group of scientists to examine some of the oldest rocks on the planet, with about 3.7 billion years. The authors concluded that these rocks contained stromatolites, stratified geological structures that, in their day, were formed by the activity of bacteria, and therefore are considered signs of the presence of life (certain bacteria are still forming that type of structure). . So we have been dating for two years the origin of life in 3.700 million years ago (800 million after the formation of the planet). And now the story has been repeated, as you can read in Subject. The Greenland stromatolites were again a deception of the stones, according to a very thorough investigation by a team from the United States and Denmark. Now we have to say again that the oldest evidences of life date from 3,450 years ago. In the case of these Australian stromatolites, the evidence of their biological origin is much stronger (in fact, they were obtained by the same team that has refuted the Greenland stromatolites).
And what? The reader will think. What else do they give a few hundred million years up or down? The answer is that the dating of the first living being affects our perception of the probability that life will evolve on other planets. This is not a serious statistical theory – with only one case in the sample, there is no way to do it – but if we knew that life was formed on Earth as soon as geology made it possible, we would tend to think that its probability is high. That's what we believed in the last decade, that we barely had a hundred million years to generate life from chemistry. With the latest data, we have almost 1,000 million years for that process. This lowers our expectations about probability. Hence the importance that experts give to these dates.
Most scientists, I would say, believe that the evolution of life is a likely phenomenon in the right astronomical circumstances, and with the amount of suns out there (200 billion stars only in our galaxy), and the great percentage of them that have planets in their orbit, the hypothesis that we are alone in the universe seems every day more extravagant. But science is a slave of the world. Only the data will give us the answer.
* THE SCIENCE OF THE WEEK is a space in which Javier Sampedro analyzes scientific news. Subscribe to the newsletter of Matter and you will receive it every Saturday in your email, along with a selection of our best news of the week.