Our earth has probably at least partly by pure coincidence so long life made possible that we humans could develop sometime. This is the result of an extensive simulation of 100.000 randomly generated planets, which Earth system scientist Toby Tyrrell of the University of Southampton used to find out how unusual Earth’s fate could be.
It is almost certainly due to chance that our home planets have not suffered the same fate as Venus or Mars, for example, he concludes. This could also complicate the successful search for extraterrestrial life on a second Earth.
Gluck or logically?
As Tyrrell now explains in the journal Communications Earth Environment of Nature magazine, it is a mystery how the Earth has remained habitable for three to four billion years, making life possible. It seems more likely that at some point it became hostile to life – as seems to have happened with Mars. For example, the luminosity of the sun had increased by 30 percent during this time, which must have extinguished all life. In addition the climate is hair-barely balanced. Until now, science had amed that stabilizing mechanisms alone were responsible for maintaining favorable conditions.
Tyrrell has used his university’s supercomputer to simulate 100.000 different planets with his university’s supercomputer to determine how often they would remain viable for three billion years if they were passed through 100 times. Until now, such simulations have been carried out only for one planet – Earth. Tyrrell now wanted to explore whether some planets remained quasi-always livable and others never did, or whether the results differed more starkly. The results were pretty clear, he explains. For most of the planets that were at least partially successful, there was only a probability, not a certainty, of maintaining livable conditions over the entire period.
Of the 100.000 simulated planets, about nine percent (8700) were able to provide livable conditions for at least three billion years. About 8000 of them, however, had succeeded in fewer than 50 of their 100 runs, he said, and about 4500 had succeeded only less than 10 times. This suggests that chance is an important factor when it comes to providing conditions worth living in over billions of years. There are also examples in the history of the Earth of conditions in which almost all life was wiped out, such as on the "Snowball Earth". There could be exoplanets, which once offered comparable conditions to our earth, but at some point became too cold or hard. That could deprive the chances of success with the search for a second earth, so Tyrrell.