Conditions for Life on Mars Persisted for Between 2.3 and 2.6 Billion Years

NASA’s Perseverance rover has discovered evidence of complex organic molecules in the samples it has collected at the Jewzero Crater on Mars. Using an instrument on board the rover known as SHERLOC, it has identified preserved organic matter that would suggest the ingredients for life similar to that on Earth was present in Mars’ past.

NASA’s other active rover, Curiosity, has identified organic matter at its landing site, the Gale Crater, indicating the presence of the building blocks for life were at some point widely distributed across the Martian landscape.

But it is the presence of aromatic organic molecules at Jezero that has led to a conclusion that the conditions for life on Mars persisted for a long period, between 2.3 and 2.6 billion years. SHERLOC found three rock surfaces with organic molecules present, and when Perseverance used its drill, identified similar molecules 8 to 10 millimetres deep within collected rock samples. Four of these samples have been stored for pickup by the future Mars Sample Return mission still in the planning stages.

The Jezero Crater has produced an abundance of organic molecules by an order of magnitude over what has been found at Gale Crater so far, proving that NASA chose well to plant Perseverance there. Much of the rock from which the organic molecules have been detected is water-altered basalt with low amounts of ferrous oxide (FeO) embedded. This reinforces the hypothesis that where there is water, that’s where we likely will find organics and life.

The discoveries of organic molecules were found in concentration in two Jezero sites. The results appear in a published article appearing July 12, 2023, in Nature, which states that the “key building blocks for life may have been present over an extended period of time” and “two potentially habitable paleo-depositional settings in Jezero crater.”

How do we know the extent of time of up to 2.6 billion years when conditions for life existed? Because basalt is an igneous rock which makes it useful for doing accurate dating. That’s what makes Jezero such an incredible site because it contains a combination of sedimentary and igneous rocks with the latter highly suitable to accurately age. As a result, we know that the lake systems that formed in Jezero existed 3.8 to 3.6 billion Earth years ago. A Martian year is almost twice as long as an Earth year so in terms of Mars’ timeline, between 1.9 and 1.8 billion Martian years ago. The interaction between free-standing water and rock would have been a comfortable environment for Martian microbes to evolve.

Could there be another explanation for the organic compounds found in these Jezero rock samples? The organics could have been brought to Mars when comets and meteorites intersected its orbit. Or the existence of organic compounds could be from inorganic chemistry with chemicals on Mars interacting with carbon dioxide (CO2) which today makes up almost the entire atmosphere of the planet.

Would Mars have been a more hospitable place over up to 2.6 billion years back in time? One thing is for sure, Perseverance tells us it was because today, free-standing water cannot be found anywhere on the planet’s surface. For it to have flowed back then, the climate of the planet had to be far more benign.

Why did it change? The lack of a strong magnetic field similar to that on Earth may be one of the reasons the Martian surface today is inhospitable. Another reason may have to do with the planet’s mass, just not big enough to hold onto a thick atmosphere to protect the surface from cosmic and solar radiation.