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On February 18, NASA’s Perseverance rover will parachute into thin Martian air, marking a new era in the exploration of the Red Planet. Landing on Jezero Crater, located north of the Martian equator, will not be easy. According to NASA, only about 40% of missions sent to Mars are successful. If so, persistence could drastically change the way we think about extraterrestrial life. That’s because scientists believe Jezero, a 28-mile-wide impact crater that was once a lake, is a great place to look for evidence of ancient microbial life on Mars.
Once arrived, Perseverance will collect and store samples of Martian rocks and soil, which will ultimately be returned to Earth. This is called a “sample return mission”, an extremely rare type of space exploration mission due to its expense. (Indeed, there has never been a sample return mission from another planet.) And once Martian soil returns to Earth in a decade, scientists will begin studying the material to determine s ‘there was ancient life on Mars.
Yet some scientists believe these samples could answer an even bigger question: Did life on Earth originate on Mars?
While the idea that life began on Mars before migrating to Earth sounds like a far-fetched science fiction premise, many leading scientists take this theory seriously. The general idea of life starting elsewhere in space before migrating here also has a name: Panspermia. It is the assumption that life exists elsewhere in the universe and that it is distributed by asteroids and other space debris.
To be clear, the notion of life on Earth coming from Mars is not a dominant theory in the scientific community, but it seems to be spreading. And scientists like Gary Ruvkun, professor of genetics at Harvard Medical School, say it seems “obvious, in a way.”
The evidence begins with how space debris moved around the young solar system. Indeed, we have evidence of an exchange of rocks from Mars to Earth. Martian meteorites have been found in Antarctica and around the world – around 159, according to the International Association of Meteorite Collectors.
“You can attribute them to Mars based on the gaseous inclusions they have, which are sort of the equivalent of the gases that were shown by the Viking spacecraft” to exist in the atmosphere of Mars, Ruvkun said. . In other words, tiny air bubbles in these rocks reveal that they were forged in Martian air. “So there is an exchange between Mars and Earth – probably more often from Mars to Earth because it’s going ‘downhill’, going to Mars is ‘upward’, gravitational.
But for Ruvkun, whose area of expertise is genomics, this is the moment of cellular life that he says makes it clear that life on Earth comes from somewhere else – maybe from Mars, or maybe of Mars facing another planet.
Ruvkun noted that our genomes reveal the history of life and provide clues to the ancestors that came before us millions, if not billions of years. “In our genomes you can kind of see the story, right?” he said. “There is the world of RNA that preceded the world of DNA and it is very well supported by all kinds of current biology; so we know the steps evolution has taken to get to where we are now.
Thanks to advances in genomics, the understanding of LUCA (the last universal common ancestor) – the organism from which all life on Earth evolved – has advanced considerably. By studying the genetics of all organisms on Earth, scientists get a very good idea of what the one-celled ancestor of all living things (on Earth) looked like. They also know the timeline: All modern life forms descend from a single-celled organism that lived around 3.9 billion years ago, just 200 million years after liquid water first appeared. In the grand scheme of the universe, it is not that long.
And the last universal common ancestor was quite complicated as far as organisms are concerned. That leaves two possibilities, says Ruvkun. “Either the evolution to modern complete genomes is really easy, or the reason you see it so quickly is that we just ‘took’ life, it didn’t really start here.” He adds, “I like the idea that we just grabbed it and that’s why it’s so fast, but I’m an outlier.”
If so, Erik Asphaug, professor of planetary science at the University of Arizona, is also an outlier. Asphaug said what we know about the oldest rocks on Earth – which have chemical evidence for carbon isotopes, dating back nearly 4 billion years – tells us that life began “to form. on Earth almost as soon as it was possible for it to happen. “
If so, it sets an interesting precedent. “Let’s say you expect life to flourish whenever a planet cools down to the point where it can start to have liquid water,” Asphaug said. “But just looking at our own solar system, which planet was likely to be habitable first? Almost certainly Mars.”
This is because, said Asphaug, Mars formed before Earth. At the beginning of Martian history, when Mars was cooling, Mars would have had a “hospitable” environment before Earth.
“If life were to start anywhere, it could start on Mars first,” Asphaug said. “We don’t know what the requirement is – you know, if it required something super special like the existence of a moon or some factors that are unique to Earth – but just in terms of where it was. first liquid water would have been Mars. “
An intriguing and compelling piece of evidence concerns how the material moved between the two neighboring planets. Indeed, the further back in time you go, the larger the rock collisions between Mars and Earth, said Asphaug. These impact events could have been huge “mountain-sized boulders of Mars” that were launched into space. These massive asteroids could serve as home to a robust microorganism.
“When you collide with a planet, a fraction of that mountain-sized mass will survive as debris on the surface,” he said. “It took a while for modeling to show that you can have a relatively intact survival of what we call ‘ballistic panspermia’ – shoot a planet, knock pieces of it over and land it on another planet.” . But it’s doable, we think it happens, and the path would tend to go from Mars to Earth, much more likely than from Earth to Mars. “
Asphaug added that surviving the trip, given the mass of the vehicle for microorganisms, would not be a problem – nor would it survive on a new hospitable planet.
“Any early life form would be resistant to what happens at the end of the planet’s formation,” he said. “Any organism that is going to exist must be used for the horrific bombardment of impacts, even outside of that, from planet to planet.”
In other words, early microbial life would have been fine with harsh environments and long periods of dormancy.
Harvard professor Avi Loeb told Salon via email that one of the Martian rocks found on Earth, ALH 84001, “was not heated during its trip to over 40 degrees Celsius and could have brought the life”.
The three scientists believe that persistence may be able to add credibility to the theory of panspermia.
“If you were to go looking for life on Mars, which we hope to do with the Perseverance rover and these other Martian adventures, I would be personally surprised if they weren’t related to life on Earth,” Asphaug said.
Ruvkun said he hopes to be one of the scientists to search for DNA when the sample from Mars hopefully returns eventually.
“Launching something from Mars is a very difficult thing,” he said.
But what would that mean for human beings and our existential understanding of who we are and where we come from?
“In that case, we could all be Martians,” Loeb said. He joked that the self-help book “Men are from Mars, Women are from Venus” was perhaps more correct than we think.
Or maybe, as Ruvkun believes, we are from a different solar system and life is just dispersing throughout the universe.
“To me, the idea that it all started on Earth, and that each solar system has its own little life evolution going on, and they’re all independent – it just seems a little silly,” Ruvkun said. “It’s so much more explanatory to say ‘no, it’s spreading, it’s spreading throughout the universe, and we caught it too, it didn’t start here,” he added. “And to this moment of the pandemic – what a great time to pitch the idea. Maybe people will finally believe it. “
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