Dirk Schulze-Makuch
Scientist Joe Kirschvink, who works at the California Institute of Technology, came up with the idea that life on Earth may have emerged on Mars at the Carl Sagan Memorial Conference organized by the American Geophysical Union in San Francisco about 20 years ago. A decade after that, Steve Benner, another well-known scientist from the Foundation for Applied Molecular Evolution, started the argument that life on Earth probably originated on Mars. So where do we stand now in the context of ‘Panspermia’ (or ‘Panspermia’), a hypothesis that suggests that life could be transported from one planet to another?
CAN LIFE HAVE BEEN TRANSPORTED TO EARTH FROM SPACE?
The idea of panspermia has existed since ancient Greece; however, suggesting that bacterial spores may be propelled from star to star by solar winds and that their journey may end on habitable planets that seed them with life. It was brought up again in the modern period in 1908 by Svante Arrhenius.
Arrhenius’ basic idea was discredited mainly because few sets of evidence appeared against him. First, given the vastness of space and the small size of the planets occupying that space, the possibility that a spore could leave a star system despite the gravitational influence of that system and eventually reach another planet, seeding one planet, seems highly improbable from a statistical standpoint. Even if this possibility does happen, it is likely that the spore will be attracted and burned by the star at the center of that solar system. Moreover, even though the spores are the dormant form of some bacteria and have a protective shell, they do not survive the time interval required to travel from one solar system to another when damage from cosmic radiation is taken into account. Keep in mind that ALH84001, the most well-known and studied Martian meteorite, took several million years to reach Earth from Mars!
Another famous scientist who supported the panspermia theory was physicist Fred Hoyle; however, the idea that disease-carrying microorganisms, such as influenza viruses, came from outer space was not biologically plausible. Disease carriers co-evolve with their hosts, and since there are no humans on other planets, it’s hard to understand how a life form from outer space could have adapted so well to infect us. In contrast, comets and asteroids carried the building blocks of life, such as amino acids, to primordial Earth. They likely played a vital role in the emergence of life on our planet and possibly other terrestrial planets.
FROM ONE PLANET TO ANOTHER
Well, just like the building blocks of life, can’t microbial organisms be transferred from one planet to another? Bacteria without a thick protective shell are very vulnerable in space, even if they only travel from one planet to another within the same star system. But what if a dormant bacterium or spore is preserved in a meteorite beneath multiple layers of rock or sediment? Since the publication of Kirschvink and Benner’s hypotheses, a lot of research has been done that suggests this is a plausible scenario. If microbes are in an asteroid, much of this microbial load could possibly survive a trip from Mars to Earth. Supporting evidence has been found in research on the Martian meteorite ALH84001, as its interior never rose above 40 degrees Celsius when it was ejected from Mars, nor when it entered Earth’s atmosphere—and remained well below its sterilization temperature.
Clearly, the proposed transfer of life between Mars and Earth requires that life on Mars must have originated there in the first place. This seems reasonable given that primordial Mars was hotter, wetter, and much more Earth-like. Life on Mars may have evolved earlier than on Earth; because it became habitable more quickly. Smaller than Earth and farther from the Sun, it cooled shortly after its formation in extreme temperatures. In contrast, Earth was hotter and additionally had to “digest” the planetary collision that created the Moon. The magma oceans that formed after this collision dominated the Earth’s surface for a long time before a habitable surface appeared on our planet.
The transfer of meteorites and life, in principle, can occur in both directions from Mars to Earth or vice versa, starting the origin of life on another planet. Still, the orbit towards Earth seems much more likely since Earth has a greater gravitational effect and the Sun is at the center of our star system. Any matter thrown into space from Mars will most likely make its way towards the Sun. Our planet, by chance, may have been in the right place to intercept the Martian rocks.
So, can we all be Martians? Given our lack of knowledge about the origin of life, we cannot say for sure. But that’s likely what happened. And that’s a hypothesis that needs to be tested on future expeditions to Mars. If we plan a life-detection mission at the earliest opportunity, we can study Martian life and organic building blocks, if any, to find the answer we’re looking for.
Original article Search for Life in the Universe taken from the website. (Translated by Tarkan Tufan)
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