Organic materials are found all over our solar system, but life so-far only exists on Earth. Our planet's early stages were complicated for the formation of life, but Mars shows evidence of much earlier readiness in the study of its rocks. While meteorites containing Martian bacteria could have initiated life, another study considers whether the meteorite impact that ended the dinosaurs could have promoted a microbial boom under the surface of its crater.
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Astro Brief is a podcast collaboration between KSMU, the Missouri Space Grant, and MSU's Department of Physics, Astronomy and Materials Science. Hosted by Dr. Mike Reed, Astro Brief focuses on astronomical events, the field of astronomy, and astronomy-related guests. It airs Thursdays at 9:45 am on KSMU.
Transcript
Could meteorite impacts actually be good for life? It turns out the answer might be yes, and we're going to discuss two possibilities.
The first involves the seeds of life.
On several programs, we've talked about organic molecules existing all over our solar system — on the asteroid Bennu, Comet Wild 2, geysers from Saturn's moon Enceladus, and of course, on Mars. So we know the raw materials are streaming all over space; it's just a question of how those materials get organized into living material, and specifically how that material appears on our Earth — the only known place to have life.
But was it the only place to have life?
The origin of life on Earth has some issues, namely that early, early Earth would have been a hotter water world with smaller volcanic hotspots. For organic materials such as amino acids, lipids, and long carbon chains of nucleic acids to get together to form the metabolic and informational systems of cells likely required wet-dry cycling, UV light, and perhaps volcanism.
Those conditions were pretty limited on the early Earth, but not so much on early Mars.
As Dr. Christopher Carr of Georgia Tech published in the journal Astrobiology in 2022, an oxidation atmosphere on Earth did not occur until the Earth was about a billion years old caused by life, whereas Mars transitioned to an oxidizing atmosphere much earlier and for multiple causes. Evidence for this has been found in 3.7 billion year-old rocks on Mars. Also Mars had a higher phosphate content which is needed to build informational polymers and to store energy in cells. Mars is 10 times less massive than our Earth and so would have cooled to a solid surface quicker and with less water blanketing its surface, it would have been a better habitat for early life to form.
But assuming Mars formed life first, how did it get here?
We do have Mars rocks on Earth in the form of meteorites. One such meteorite famously has fossilized bacterial shapes — though they may have been caused by non-biological processes. So we know that if asteroid impacts on Mars are powerful enough, Martian rocks get ejected into space. As Mars has one-third the gravity we do, this is an easier process. We also know that the vacuum and cold of space is not the great sterilizer we once thought it to be. So Martian rocks containing life could have traveled for millions of years before happenstance had them cross early Earth's path, sending it with Martian life to develop into us.
This process of seeding us from Mars is known as Lithopanspermia. As Dr. Carr writes, "Such a history, while incredible, is a story of our past that is consistent with the available genetic and geological evidence.".
Our second example is even more surprising — at least to me as I wouldn't have even considered it.
And that is, the six-mile diameter meteorite that impacted the Earth 66 million years ago — wiping out the dinosaurs — could have benefited microbial life. Consider that the impact which created the Chicxulub crater made a giant tsunami, created a global firestorm, and put so much dust into the atmosphere that it created what's called an impact winter. All this combined wiped out 75% of all species on Earth, but beneath the surface it was creating the conditions for life to thrive.
The impact created a huge system of shattered rock tens of miles across and underground water would have become superheated, flowing through and interacting with the rock — exactly the sorts of systems with the right chemistry and energy source to produce life. Of course Earth already had life then, but perhaps it fostered a growth and expansion of species and if it can happen on Earth, it could also happen elsewhere.
And could it have been sites where life originated on Earth, if not Lithopanspermia from Mars?
A recent paper published in Nature: Communications Earth & Environment by Dr. Ann Marie Pickersgill of the University of Glasgow and collaborators examined how long the Chicxulub crater would have created a good environment for life. The question is whether such systems could remain sufficiently long that the chances of generating life are reasonable. Dr. Pickersgill's team estimate it endured for around 8 million years — a very interesting find.
Of the roughly 200 impact structures on Earth, 70 of them show signs for hydrothermal systems like under the Chicxulub crater — and of those, 8 show clear evidence that microbial life colonized them.
Did life on Earth originate under a crater, or seeded by a cratering Martian meteorite?
Unfortunately, there's no original Earth rock left to check, but if we do find life on Mars, we could cross-reference its DNA with ours. And who knows — maybe we would be distant, distant relatives.