We are about two weeks away from NASA’s Perseverance Rover landing on Mars in Jezero Crater. This particular site was picked because it appears, in satellite imagery, to be a former lake bed, and is just the kind of place where, if Mars had life, we might expect to find fossils.

Yes, folks, Percy is going fossil hunting.

The problem is, even if Percy finds what appears to be fossilized bacteria, it will be hard to verify that what it sees is evidence of life and not a look-alike chemical reaction. Just how hard it will be was brought home by a new research study published in the journal Geology. Experiments by geobiologists Julie Cosmidis, Christine Nims, and their colleagues found that random chemical reactions left in the residue of their lab equipment closely resemble bacteria, and these structures can be fossilized very easily.

According to Nims: …under the microscope, you could see these beautiful structures that looked microbial. And they formed in these very sterile conditions, so these stunning features essentially came out of nothing. It was really exciting work. 

Cosmidis goes on to explain: We thought, ‘What if they could form in a natural environment? What if they could be preserved in rocks?’ We had to try that, to see if they can be fossilized.

The team called these structures biomorphs — shapes that look biological. They simulated the formation of silica-rich rocks with fossils by carefully mixing silica solution and the biomorphs under conditions that mimicked those found when fossils form. According to a release related to this paper: They found not only that they could be fossilized, but also that these [biomorphs] were much easier to preserve than bacterial remains. The [biomorphs] ‘fossils,’ structures … were more resilient and less likely to flatten out than their fragile biological counterparts.

Cosmidis puts it this way: Microbes don’t have bones. They don’t have skins or skeletons. They’re just squishy organic matter. So to preserve them, you have to have very specific conditions, so it’s kind of rare when that happens.

If biomorphs can be created by accident in the residue in labware and easily fossilized, this raises the disturbing possibility that we are going to find a whole lot of fossilized biomorphs, which are not life, in the mix with whatever extremely rare, actually fossilized bacteria may be out there.

We already knew this could be a problem. About twenty years ago, researchers found what they said could be fossilized nano-bacteria in a Mars meteorite, and in the months and years after their announcement, teams the world over have found ways to explain their results as anything except life.

I personally am hopeful that Percy will find something fairly uncontroversial. I’m wishing for a nice, beautiful collection of stromatolites — fossilized bacterial mats like we see here on Earth. To be fair, anything we find will have folks arguing, “That can’t be fossilized life because…”, but if we can show that life here is similar to what began out there, far across the solar system, it will give us a new understanding of how life might fight to survive out there beyond the heavens.

More Information

GSA press release

“Organic biomorphs may be better preserved than microorganisms in early Earth sediments,” Christine Nims et al., 2021 January 27, Geology