Ancient Jezero Crater is depicted in this artistic view, replete with shoreline of a lake that dried up billions of years ago.
Credit: NASA/JPL-Caltech/MSSS/JHU-APL

As the full-stop destination of NASA Perseverance’s journey from Earth to Mars, the mega-rover is slated to set down within Jezero Crater – a lake in the Red Planet’s ancient past, a place that sports a shoreline that dried up billions of years ago.

On ancient Mars, water carved channels and transported sediments to form fans and deltas within lake basins.

Wheeling itself around that aeon-aged geological site, scientists are eager to visit its shoreline because it may have preserved fossilized microbial life, if any ever formed on Mars.

Illustration shows NASA’s Perseverance rover exploring inside Mars’ Jezero Crater, a 28-mile-wide (45-kilometer-wide) feature believed to an ancient lake-delta system in a hunt for signs of past microscopic life.
NASA/JPL-Caltech

False positives

Here on Earth, life has been found to have evolved in some of the most extreme environments. But what about Mars?

New research suggests that organic biomorphs may be better preserved than microorganisms in early Earth sediments. However, experiments show the record of early life on Earth could be full of “false positives.”

That’s the topic of a recent research paper that cautions about encountering “fools gold” in appreciating the task of identifying fossil microorganisms that are among the oldest traces of life on Earth.

“The objects we described in the paper — “organic biomorphs” — are quite small, in the micrometer size range, just like bacteria, The current rover missions, including Perseverance, are not equipped to see objects that are this small,” explains Julie Cosmidis, co-author of the paper and an associate professor of geobiology within the Department of Earth Sciences at the prestigious University of Oxford in England.

Perseverance rover deposits select rock and soil samples in sealed tubes on Mars’s surface for future missions to retrieve and bring back to Earth for detailed study.
NASA/JPL-Caltech

Sentiment about sediment

“The only way we will be able to observe biomorphs or actual fossil bacteria on Mars is to wait for returned samples,” Cosmidis told Inside Outer Space. “Chemically, the biomorphs are made of organic matter. The presence of organic matter in Mars sediment has already been demonstrated. We don’t know whether this organic matter is biogenic [resulting from the activity of living organisms] or not.”

Cosmidis added that the kind of biomorphs described in their research paper cannot form on Mars today. That’s because Mars now is lacking the key chemical needed for their formation: sulfide. The biomorphs are indeed formed by reacting organics with sulfide.

On the scene. NASA’s new robotic Mars explorer, the Perseverance rover.
Credit: NASA/JPL-Caltech

Evidence for interactions

“But we now have evidence that sulfide was present on early Mars: past missions have shown that ancient Mars sediments record evidence of sulfur redox cycling, including the presence of sulfide,” Cosmidis points out. There’s an abundance of organosulfur compounds in ancient Martian sediment, which is again evidence for interactions between organics and sulfide – and that is exactly the type of reaction that produces the biomorphs. 

“So, I think these biomorphs could have formed on early Mars, but what I don’t know is whether or not they could have been preserved in Martian sediments until now,” Cosmidis adds.

Meteoritic Mother of Invention and controversy: The Mars rock, ALH84001.
Credit: NASA

It is the opinion of Cosmidis that it is very important that Mars scientists find out, and also how to better discriminate biomorphs from “real” fossil bacteria, “if we want to avoid repeating the ALH84001 fiasco once we have returned samples.”

Allan Hills 84001 (ALH84001) is a fragment of a Martian meteorite recovered here on Earth. The specimen has been the subject of a debatable scientific claim that it contains the vestiges of ancient life indigenous to Mars.

Jezero Crater – home base for Perseverance rover.
Credit: NASA/JPL-Caltech/MSSS/JHU-APL

 

 

 

Meanwhile — and if successful in its landing and wheeling about — what will the Perseverance rover discover at Jezero crater?

 

For access to the instructive paper – “Organic biomorphs may be better preserved than microorganisms in early Earth sediments” – go to:

https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G48152.1/594307/Organic-biomorphs-may-be-better-preserved-than

Leave a Reply