NASA’s most specialised life-hunting laboratory up to now is at present hurtling towards the Pink Planet, the place it would try a touchdown subsequent week. After the crimson mud settles, if all goes in response to plan, the Perseverance rover will begin rolling alongside dried-up riverbeds within the first direct try but to deal with the query driving a lot of the Martian exploration program: Is there, or was there, life on Mars?
Perseverance received’t ship a transparent reply any time quickly, however as outcomes trickle again to Earth over the approaching years, a small group of planetary scientists can be expecting hints of an much more alien concept. Possibly, simply perhaps, life on Earth got here from Mars.
“There’s a lot of issues which have come to gentle solely not too long ago, which strongly assist no less than the plausibility of an origin of life on Mars and its potential switch to Earth,” says Christopher Carr, a planetary scientist and the Georgia Institute of Know-how, who not too long ago printed an unreviewed preprint reviewing the speculation.
In latest a long time, biologists have reconstructed nice swaths of the household tree that relates all recognized organisms. Fossils recommend that human beings and apes shared a standard ancestor as not too long ago as 13 million years in the past, and that whales, bats, and people all shared parentage roughly 65 million years in the past. The final common frequent ancestor (LUCA)—a microbial Adam or Eve—doubtless lived in a sea vent roughly 4 billion years in the past, genetic analyses have prompt.
And there the path goes chilly. Detailed genetic data peter out on the base of the tree of life. LUCA’s opponents might have survived a while as fossils, however the planet’s tectonic churn has lengthy since demolished its earliest rocks. All biologists know for positive is that Earth shaped round 4.5 billion years in the past, after which half a billion years later LUCA lived. The way it developed, and the place its forerunners got here from, is up for debate.
Maybe, Carr and some others have imagined, LUCA was the descendent of microbial Martian invaders touring by asteroid. The speculation shouldn’t be extensively accepted. However Carr advances two the reason why a Martian origin for all times is value speculating about.
Carr says natural molecules “rain down mainly in all places” all through the universe. However nobody is aware of which particular chemical reactions fused natural molecules into the assorted constructing blocks wanted to assemble cells on Earth. One outstanding recipe holds that the friendliest setting for cooking up life is on land in shallow swimming pools of water, the place ultraviolet gentle, evaporation, precipitation, and warmth from volcanoes or asteroid impacts might fire up the substances in the precise methods (though many researchers imagine deep sea vents make a compelling various possibility).
Early Earth, nevertheless, was drowning in water. Three and a half billion years in the past, all however a pair p.c of the Earth’s floor was deep underwater, researchers have estimated, and LUCA lived far earlier than that. In the meantime, younger Mars was soggy however not soaked, probably providing way more alternatives for all times to get began.
The second clue comes from a doable sample in amino acids, the constructing blocks cells use to assemble the proteins they should function and survive. All LUCA descendants make their molecular equipment from the identical 20 molecules, although most fashionable proteins might conceivably work with about half of that repertoire. The much less essential amino acids appear to assist organisms cope with oxidation, a 2018 research concluded, hinting that LUCA’s forerunners included them whereas evolving in an setting wealthy in oxygen or different oxidizing compounds.
However Earth was oxygen-free for its first 2 billion years, so how did LUCA come by its oxidation-friendly amino acids? The roots of its household tree, Carr suspects, might stretch again to Mars, the place oxidizing circumstances developed earlier. Rising there, life might have caught a experience to Earth on one of many many asteroids exchanged between the 2 planets.
Different origins of life researchers, nevertheless, doubt that the challenges to life arising on Earth are grave sufficient to resort to interplanetary journey. The younger Earth lacked continents, however Hawaii-like islands doubtless offered greater than sufficient actual property for all times to take maintain, in response to Nicholas Hud, a biochemist additionally at Georgia Tech however who was not concerned within the latest analysis. Moreover, he suspects organisms might have adopted the extra amino acids for causes unrelated to oxidation.
Numerous researchers have made arguments for Mars as soon as being a friendlier setting for all times than Earth over time, however Hud hasn’t but come throughout one he thinks is compelling. “I discover [moving the origin of life to Mars] to be a bit of too dramatic,” he says. “Possibly we simply want to know among the chemistry higher. Possibly our mannequin for the early Earth isn’t pretty much as good correctly.”
Perseverance received’t discover life on Mars subsequent week, however its observations will, on the very least, start to assist researchers refine their understanding of early Mars. Because the rover explores Jezero Crater, which as soon as collected muddy waters from everywhere in the space, its devices might be able to higher decide when Mars began to rust (or oxidize) by analyzing floor deposits (and see whether or not the onset of oxidation matches the inferred date for when pre-Earth life crafted its nonessential amino acids).
Finally, Carr hopes to sometime ship an instrument to Mars that would settle the controversy: a gene sequencer to detect genetic materials from present Martian life (if it exists) and examine if it connects with our tree of life. Carr is a member of MIT’s Seek for Additional-Terrestrial Genomes, a challenge engaged on simply such a machine, and he says that after years of growth their system is nearing flight readiness. The laborious half can be discovering dwelling Martian microbes to investigate, on condition that the comfiest spots on fashionable Mars lie deep beneath the floor.
“This could actually be achieved on a future Mars mission,” Carr says, even when it’s a problem.