mars rocks
The solid surface of Mars formed 100 million years before Earth's - meaning life would have had a head start to evolve on the Red Planet.

Early Mars, like the other rocky planets, was covered in a global magma ocean. The top of that sea of molten rock eventually hardened to a crust, but we weren't sure exactly when - researchers thought it could have happened between 30 million and 100 million years after the start of the solar system. Now, we have evidence that it was much faster.

Laura Bouvier at the University of Copenhagen in Denmark and her colleagues figured this out by studying ancient crystals in a Martian meteorite found in Morocco in 2011, dating them to about 4.4 billion years old.

Based on the compositions of the crystals, the researchers suggest that Mars first formed a crust about 4.5 billion years ago. This initial surface survived for about 100 million years before parts of it were melted again, possibly by impacts, to create the magma that the zircons came from.

Mars before Earth

That means Mars was formed and its magma ocean was solidified within 20 million years after the birth of the solar system.

"This shows that Mars was actually clement and therefore habitable maybe 100 million years before Earth was," says Lindy Elkins-Tanton at Arizona State University, who was not involved in the research. "Mars totally got the head start on creating life, if indeed it ever did."

A thick atmosphere would slow down the solidification of the magma ocean, so these observations may help set constraints on the thickness and water content of Mars' early atmosphere, she says. Plus, if we ever do find signs of past life on Mars, understanding when the crust formed will help us figure out the timeline of when that life could have arisen.

Journal reference: Nature, DOI: 10.1038/s41586-018-0222-z