A new climate modeling study suggests that ancient microbes caused a climate change on Mars that made the planet less habitable, possibly leading to their extinction.
The article was published in the journal Nature Astronomy .
According to the study, simple microbes that feed on hydrogen and emit methane may have flourished on Mars around 3.7 billion years ago, around the same time that primitive life took hold in Earth’s primordial oceans.
But while on Earth the emergence of simple life gradually created an environment conducive to more complex life forms, the exact opposite happened on Mars, according to a team of scientists led by astrobiologist Boris Sauterey of the Institut de Biologie de l’Ecole Normale Supérieure (IBENS) in Paris.
Sautray and his team ran sophisticated computer simulations that simulated the interaction of what is already known about Mars’ ancient atmosphere and lithosphere with hydrogen-consuming microbes like those that existed on ancient Earth.
The researchers found that while on Earth, the methane produced by these microbes gradually warmed the planet, Mars instead cooled, driving the microbes deeper and deeper into the Earth’s crust to survive.
“At that time, Mars was relatively humid and relatively warm, between minus 10 and 20 degrees Celsius. On its surface was liquid water in the form of rivers, lakes, and possibly oceans. But its atmosphere was very different from Earth’s,” the scientist said.
Being farther away from the Sun than Earth, and therefore naturally colder, Mars needed these greenhouse gases to maintain a comfortable temperature for life.
But when these early microbes began to consume hydrogen and produce methane (which acts as a powerful greenhouse gas on Earth), they actually slowed down this warming greenhouse effect, gradually making ancient Mars so cold that it became inhospitable.
As the planet cooled, more of its water turned to ice and surface temperatures dropped below minus 60 degrees Celsius, pushing microbes deeper and deeper into the crust, where warmer conditions persisted.
While the microbes may have originally lived comfortably just below the sandy surface of Mars, over the course of a few hundred million years they were forced to retreat to depths of more than 1 km, simulations have shown.
Sautray and his team identified three places where traces of these ancient microbes were most likely preserved closer to the surface.
These locations include Jezero Crater, where the NASA rover is currently hunting for rock samples that may contain traces of this ancient life, and two low-lying plains: the Hellas Plain in the mid-latitudes of the southern hemisphere and the Isidis Plain north of the Martian plain.