Nobody is sure how life emerged from the primordial chemistry of Earth. But now we have more evidence that Earthlike life could have evolved on Mars.
Illustration of Mars today and Mars several billion years ago, by Kevin Gill
It all has to do with phosphates, minerals that are crucial for building DNA, cell membranes, and many other parts of our bodies. On the early Earth, billions of years ago, these minerals were locked up in rocks. Over millennia, water ate away at those rocks, eventually dissolving enough free-floating phosphates into the oceans that they became the building blocks of life.
But Mars has a different set of phosphates in its rocks. These phosphates, such as merrillite, don't exist on Earth — except in meteorites that have come from Mars. Martian phosphates dissolve at about 45 times the rate of Earthly ones. In other words, there would have been a lot more free-floating phosphates in the oceans of early Mars.
In a paper published today in Nature, a group of geologists and chemists from the University of Las Vegas, Nevada, explain that phosphates would have been much more available for proto-life on Mars than they were on Earth. They discovered this by recreating the conditions that would have existed on Mars, where groundwater was eating away at merrillite and other fast-dissolving phosphates. Below is a chunk of the extraterrestrial mineral merrillite that they cooked up in the lab.
They concluded that these kinds of chemical reactions could have accelerated abiogenesis, or the process of life emerging from inanimate chemicals:
Our experimental ﬁndings predict phosphate release rates during water–rock interactions on Mars that are as much as 45 times higher than on Earth and phosphate concentrations of early wet martian environments more than twice those of Earth. We suggest that available phosphate may have mitigated one of the hurdles to abiogenesis on Mars.
In some ways, it would have actually been easier for life to emerge on Mars than it would have been on Earth. This raises the question of whether life did, in fact, evolve on Mars and come over to Earth in meteorites — the same way that merrillite arrived.
Scientists who subscribe to the panspermia theory would say this is a good possibility. This theory suggests that life came to Earth from another world. Many scientists would say it's plausible that the building blocks of life could have arrived on Earth via meteorites from Mars.
Over at New Scientist, Lisa Grossman explains that there are even competing theories about how life could have originated on Mars and come to Earth. The more we learn about Martian geology, the more it seems that conditions were ripe for life to emerge on the planet during its early days. The question is really what role water would have played. Writes Grossman:
Chemist Steve Benner gave [a talk] this week at the Goldschmidt conference of geochemists in Florence, Italy. Benner, of the Westheimer Institute of Science and Technology in Gainesville, Florida, argued that early Mars, not Earth, was a better chemical cradle for producing RNA molecules.
According to Benner, young Mars would have had an abundance of oxygen in its atmosphere, which would have reacted with boron and molybdenum to make oxidised versions of these elements. The compounds could then act as catalysts that guided the formation of RNA. The molecules of life, or even hardy simple organisms, could then have been transferred to Earth via meteors. Benner's scenario requires Mars to be a desert, because RNA falls apart if you try to build it in water.
But his scenario does not address where the phosphate in Martian RNA came from. Adcock's proposal, meanwhile, requires an ocean to dissolve the phosphate minerals, but doesn't say how you then stop RNA from destabilising in water.
These are similar questions to what scientists ask about how life emerged on Earth. So if we are able to determine that life emerged on Mars, we won't have answered the fundamental question of how inanimate chemicals become living cells. We'll have simply pushed those questions onto Mars, whose early geochemistry is just as mysterious as the Earth's.
Still, it would be a great leap forward scientifically — and just plain awesome — if we could say that we're all Martians.
Sources linked in the text.
Annalee Newitz is the author of the book, Scatter, Adapt and Remember: How Humans Will Survive a Mass Extinction. Follow her on Twitter.