After a Nature paper provided possible indications of past life on Mars, neuroscientist and philosopher Erik Hoel makes the case that Mars could act as a planetary museum for life’s origins. For example, Mars has no plate tectonics to bury the possible signs of life captured by NASA, no foundations laid over it, no footsteps trampling it… and so the so-called “leopard spots” suggesting mineral leftovers of long-dead microbes are effectively untouched and frozen in time. Hoel argues we must go to Mars to investigate; not only as a scientific pursuit, but as an existential one.

We are not low creatures.

This is what I have been thinking this week. Even though humanity often does, at its worst, act as low creatures.

Some act like vultures, cackling over the dead. Or snakes, who strike to kill without warning, then slither away. Or spiders, who wait up high for victims, patient and hooded and with the blackest of eyes.

But as a whole, I still believe that we are not low creatures. We must not be low creatures. We simply need something to help us remember.

An arrow-shaped rock on Mars, only a few feet across, and found sitting at the bottom of an ancient dried-up river, helped me remember. For, on Wednesday, and therefore lost amid the news this week, a paper was published in Nature. It was the discovery that—arguably for the first time in history—there are serious indications of past life on Mars.

Specifically, these “leopard spots” were analyzed by the rover Perseverance.

Figure 1: Mars leopard spots. Photo by NASA.

According to the paper, these spots fit well with mineral leftovers of long-dead microbes:

Minerals like these, produced by Fe- and S-based metabolisms [iron and sulfur metabolisms], provide some of the earliest chemical evidence for life on Earth, and are thought to represent potential biosignatures in the search for life on Mars. The fact that the reaction fronts observed in the Cheyava Falls target are defined by small, spot-shaped, bleached zones in an overall Fe-oxide-bearing, red-coloured rock invites comparison to terrestrial “reduction halos” in modern marine sediments and “reduction spots,” which are concentrically zoned features found in rocks of Precambrian and younger age on Earth.

It matches with what we know about some of the oldest metabolic pathways here on Earth, and there are not many abiotic (non-biological) ways to create these sorts of patterns; of those abiotic ways (the null hypothesis), there is no evidence right now that this rock experienced those.

Maybe this helps people contextualize it: If this exact same evidence had been found on Earth, the conclusion would be straightforwardly biological, and an abiotic explanation would be taken less seriously—such a finding would likely end up in textbooks about signs of early life on Earth and used to argue for hypotheses about how life evolved here. Remember, without fossils, all we have are similar traces of the early life on Earth. What are cautiously called “biosignatures” on Mars are the exact same kind of evidence we accept about our own pre-fossil past (in fact, this is arguably better evidence than what we have on Earth if you compare like-to-like cases and factor in the instrument differences and limitations).

Unlike other recent, and far more controversial claims of alien life (e.g., statistically debatable signs of potential biosignatures on extrasolar planets light-years away, or Avi Loeb’s ever-changing hub-hub around an extrasolar comet), the scientists in this case have been very conservative and careful in their language, as well as their scientific process.