Modelling showed that conditions beneath the surface of young Mars were as comfortable for primitive life as those in the oceans of young Earth. However, this did not last long and microbial activity quickly depleted the atmosphere, rendering the planet uninhabitable.
Today's Mars is a harsh desert, dry and cold, but it wasn't always like this. In the distant past, the neighbouring planet was comparatively warm and humid, surrounded by a fairly dense atmosphere rich in carbon dioxide and hydrogen, and primitive life may well have arisen under such conditions. A new paper published in Nature Astronomy also says this. "Conditions beneath the surface of early Mars may have been suitable for the existence of methanogenic microbes," stressed the paper's key author, University of Arizona professor Regis Ferriere.
On Earth, such micro-organisms obtain energy without oxygen, such as from carbon dioxide and hydrogen, and methane is a by-product of these reactions. They are thought to be among the oldest, although in current circumstances they are not as ubiquitous, often inhabiting the most extreme ecological niches - like the 'black smokers' at the bottom of the oceans. However, on early Mars, about four billion years ago, during the Norse period, conditions were far more suitable for methanogenic life.
"We believe that at that time Mars was slightly colder than Earth and nowhere near as cold as it is today, with average temperatures slightly above freezing point for water," says Régis Ferrier. - We see early Mars as a rocky planet with a porous crust covered with liquid water that formed lakes and rivers, perhaps even seas and oceans."
Ferrier and his colleagues modelled the Red Planet's climate in the Norse period, taking into account the abundance and high salinity of water (as indicated by analysis of ancient Martian rocks), the porosity of the surface, and the carbon dioxide and hydrogen-rich atmosphere. Scientists used these results to model the dynamics of ecosystems. The work made it possible to assess the possibility of life existence and development deep beneath the surface of Mars. The answer was positive: such conditions could support the existence of methanogens (as also indicated by some previous work).
According to scientists, it was too cold on the planet's surface itself, but temperatures just below remained comfortable enough, and the water, carbon dioxide and hydrogen seeping in from above provided enough resources to extract energy through methanogenesis. They estimated that optimal conditions persisted at depths of up to several hundred metres. "We found the very likely existence of subsurface life, which was limited only by the spread of ice (at the surface. - Ed.) Biomass productivity may have been comparable to that of the oceans of early Earth," Ferrier added. However, this did not last long.
Simulations have shown that while at first methanogenic life on Mars may have thrived, it gradually had an increasingly negative impact on the conditions of their own existence. The biological activity of such microorganisms rapidly - over hundreds or even tens of thousands of years - altered the composition and reduced the density of the Martian atmosphere. Its hydrogen content was rapidly decreasing, which could lead not only to an energy deficit, but also to a cooling of the entire planet. As a result, Mars rapidly froze and became uninhabitable. Life was able to escape deeper and deeper into the bowels of the planet until conditions there became totally unsuitable for it as well.