The means by which Mars potentially lost its thick, carbon dioxide (CO2)-rich atmosphere are revealed in Nature Communications this week. The findings represent the first direct evidence for the process of carbonation on the Red Planet, something that is common on Earth today.

Carbonation is a widespread mineralogical process on Earth, whereby CO2, liquid water and olivine minerals react and result in CO2 in the atmosphere being sucked down and stored as carbonate in the Earth’s crust. It is proposed that Mars may have lost its formerly thick, CO2-rich atmosphere in a similar way. In order to discover whether this is indeed the case, Tim Tomkinson and colleagues examined the minerals preserved in Lafayette, a Martian meteorite that crashed to Earth around 3,000 years ago. Lafayette formed part of the Red Planet’s crust around 1,300 million years ago, when sparse amounts of liquid water existed in the planets crust. The team use electron beams to analyse the meteorite mineral composition and show that silicate minerals, such as olivine and feldspar, interacted with CO2-rich liquid water to form carbonate, which replaced some of these minerals.

Although the Lafayette meteorite comes from a time on Mars when the atmosphere was already thin, the team believe that this process was likely widespread 3,000 million years earlier, when Martian waters were charged with CO2 from a much thicker atmosphere.