ZAP // Dall-E-2
How did life on Earth begin? Although scientists have theories, they still do not fully understand the exact chemical steps that led to biology, nor when the first primitive life forms emerged.
What if life on Earth had not originated here? If I had, instead, arrived in meteorites coming from Mars?
Not the most accepted theory for the origin of life, but it remains an intriguing hypothesis. In an article on , Sean Jordanprofessor of chemistry at the University of Dublin, analyzes the arguments for and against.
Chronology is a decisive factor. Mars formed about 4.6 billion years ago, while Earth is slightly younger at 4.54 billion years old. Initially, the surfaces of both planets were in a state of fusionbefore gradually cooling and solidifying.
In theory, life could have arisen independently on Earth and Mars shortly after its formation. And although the surface of Mars today is probably uninhabitable for life as we know it, the early mars It would have had conditions similar to those on the primitive Earth.
Ancient Mars is thought to have been in the form of oceans, rivers and lakes. It may also have been geothermally active, with many hydrothermal vents and hot springs capable of offering the necessary conditions for the emergence of life.
However, about 4.51 billion years agoa rocky planet with dimensions similar to those of Mars, called Theaia.
The impact of this collision caused both bodies to merge and then separate, giving rise to the Earth. If life had already begun before this event, I certainly wouldn’t have survived.
Mars, for its part, probably did not go through an episode of global remelting. The planet suffered many impacts in the violent early Solar System, but evidence suggests that none of them were big enough to completely destroy the planet — and some regions may have remained relatively stable.
Thus, if life had emerged on Mars shortly after the planet’s formation, 4.6 billion years ago, could have continued to evolve without major interruptions during at least half a billion years.
Afterwards, the Martian magnetic field collapsed, marking the beginning of the end of Martian habitability. The protective atmosphere disappeared, leaving the surface exposed to freezing temperatures and ionizing radiation from space.
A matter of time
And on Earth, How long did it take for life to appear? after the brutal impact that formed the Moon?
Going back to the root of the tree of life takes us to a microorganism called LUCA — the . This is the microbial species from which it descends all current life.
A published in 2024 in Nature Ecology & Evolution reconstructed the characteristics of LUCA using genetics and the fossil record of primitive life on Earth. From there, he inferred that LUCA lived 4.2 billion years ago — sooner than some previous estimates.
LUCA was not the first organism on Earthbut rather one of several species of microbes that coexistence on the planet at that time. They competed, cooperated, and survived the elements while defending themselves from virus attacks.
If small but relatively complex ecosystems existed on Earth around 4.2 billion years ago, then life would have had to emerge sooner. But the sooner?
The new estimate for LUCA’s age points to 360 million years after the formation of the Earth and 290 million years after the impact that gave rise to the Moon.
All scientists know is that, over these 290 million years, the chemistry somehow became biology. Would it have been enough time for life to emerge on Earth and then diversify into the ecosystems already present when LUCA lived?
A Martian origin for terrestrial life get around this issue. According to the hypothesis, species of Martian microorganisms could have traveled to Earth in meteorites, arriving in time to take advantage of the mild conditions that followed the formation of the Moon.
Temporal coincidence may be convenient for this idea. Still, as someone who works in this field, Seán Jordan believes that 290 million years is more than enough so that chemical reactions produce the first living organisms on Earth and so that, later, biology diversifies and become more complex.
Survive the trip
LUCA’s reconstructed genome suggests it could feed on molecular hydrogen or simple organic molecules.
Together with other evidence, this indicates that the habitat of LUCA would have been a shallow marine hydrothermal vent system or a hot geothermal spring. The dominant idea in research into the origin of life is that these environments on early Earth met the necessary conditions for life to emerge from non-living chemistry.
LUCA also had biochemical machinery capable of protecting you from high temperatures and ultraviolet radiation — real dangers in these primitive environments.
But It’s far from right that early life forms could survive a trip from Mars to Earth. And there is nothing in LUCA’s genome to suggest a particular adaptation to “space travel”.
To reach Earth, microorganisms would have to survive the impact initial on the surface of Mars, to a high-speed ejection through the Martian atmosphere and crossing the vacuum of spaceunder bombardment by cosmic rays, for at least the better part of a year.
Afterwards, they would still have to resist the entry the high temperature in the Earth’s atmosphere and a new impact on the surface. This last event could, or could not, place them in an environment minimally compatible with their adaptations.
A The probability of all this happening seems very lowsays Seán Jordan. As difficult as the transition from chemistry to biology may seem, it seems to me much more plausible than the idea of this transition occurring on Mars, of life forms surviving the trip to Earth and then adapting to a completely different planet.
Still, Jordan admits he could be wrong — and thinks it’s worth looking at studies on the ability of microorganisms to survive on a journey between planets.
So far, everything indicates that only the most resistant microorganisms could withstand the crossing between Mars and Earth — species adapted to avoid radiation damage and capable of surviving desiccation through the formation of spores.
But maybe — just maybe —if a population of microorganisms were trapped inside a sufficiently large meteorite, could be protected many of the harshest conditions in space.
Some computer simulations even support this hypothesis. More simulations and laboratory experiments are underway to test it.
And this raises another question: if life arrived from Mars to Earth in the first 500 million years of the Solar System, Why didn’t it spread? from Earth to the rest of the Solar System over the next four billion years?
Maybe we’re not Martians after allJordan concluded.
