Our earth made life possible at least partly by pure chance so long that at some point we humans could develop. This is the result of an extensive simulation of 100. 000 randomly generated planets , with which earth systems scientist Toby Tyrrell of the University of Southampton wanted to find out how extraordinary the fate of the earth could be.

It is almost certain too due to coincidence that our home planets did not fare like Venus or Mars, for example, he concludes. That could also make the successful search for extraterrestrial life on a second earth more difficult.

Luck or consequential? As Tyrrell now in the trade journal Communications Earth & Environment from Nature magazine explains that it is a mystery how the earth remained habitable for three to four billion years, i.e. how it made life possible. It seems more likely that it would have become hostile to life at some point – as it seems to have happened with Mars. For example, the luminosity of the sun has increased by 30 percent during this time, which could have extinguished all life. In addition, the climate is perfectly balanced. So far, science has assumed that stabilizing mechanisms are solely responsible for maintaining the favorable conditions.

To fathom this question, Tyrrell with the supercomputer of his university 100. 000 simulated different planets in order to find out how often they would remain worth living for three billion years with each 100 runs. So far, such simulations have only ever been carried out for one planet – Earth. Tyrrell now wanted to find out whether some planets were almost always worth living and others never, or whether the results differed more. The results were pretty clear, he explains. For most of the at least partially successful planets there was only a probability, but no certainty, of maintaining livable conditions over the entire period.

Of the 100. 000 simulated planets could therefore be about nine percent (8700 ) provide living conditions for at least three billion years. About 8000 of them are in less than 50 their 100 runs have been successful, round 4500 even only less than 10 Times. This suggests that coincidence is an important factor when it comes to delivering conditions worth living in over billions of years. In the history of the earth there are examples of conditions in which almost all life was exterminated, for example on “snowball earth”. So there should be exoplanets that once offered comparable conditions to our earth, but at some point became too cold or hot. That could cloud the chances of success in the search for a second earth, according to Tyrrell.

(mho)