Did you know that terrestrial life with significant probability could have originated on Mars rather than on Earth? But you, of course, need the details: how dangerous was the journey of "life" from one planet to another astride a meteorite? We seem to be ready to answer this question.
Some things about early Earth history are odd. For example, ribose, without which ribonucleic acids are inconceivable, including those that are considered the basis of life … If you try to collect ribose from the components available on the young Earth, you will get only dirt from organic molecules, insoluble in water. Ribose, on the other hand, is soluble.
But to get it from the same components, you have to add boric acid salt or molybdenum oxides. They were on Mars, but on our planet billions of years ago they were not found - at least on the surface.
Why, the very names of the initial geological epochs of the Earth and Mars eloquently make it clear what the situation was then. Catarchaeus, called "Gadey" in English, derives his middle name from Hades, the Kingdom of the Dead. Noah's epoch on Mars, on the contrary, is why Noah's epoch is called, as it is believed that at that time there was a certain amount of water on the surface of the Red Planet (although not as much as in your homeland).
Joseph Kirschvink of the California Institute of Technology (USA) emphasizes that such minerals, in principle, can only form in desert, dry conditions. However, the early Earth, according to modern ideas, was rather wet: almost all of its surface could be hidden under water at that time, because plate tectonics with a thin and relatively warm crust could not develop, which prevented the formation of deep reservoirs that concentrate water within their boundaries …
Meteorites of Martian origin older than a certain age indicate that Mars once had a stronger magnetic field; the scientist connects this with the possibility of the existence of a serious ozone layer there. Considering the height of the Martian volcanoes and the relatively small thickness of the atmosphere, such an ozone layer could oxidize a number of surface materials that, during erosion processes, fell into the lower regions, where the catalysis process could begin, triggering the formation of … or even the same ribose.
Okay, let's say life did start on Mars. What will happen to her during "interplanetary flights"? The mechanism of the latter is obvious: to this day, asteroids, falling on the planet, are much to knock out of it a piece of rock with live bacteria or even heroic tardigrades.
But these pieces are experiencing terrible stress and heating? Yes, but impact tests have shown: the same microscopic algae can withstand collisions at speeds up to 7 km / s, and a large part of them is alive and well after that.
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Although for us 50 million km separating the Earth from the fourth planet seems to be a huge distance, by cosmic standards, Earth and Mars are neighbors in a communal apartment. Calculations show that just nine months after the asteroid hit Mars, living organisms thrown into space by the impact could reach Earth. If, of course, these organisms were on Mars.
But what about the inevitable heating? The Earth's atmosphere is dense, and the Martian meteorite entering it, it would seem, should be heating up …
A group of researchers led by Mr. Kirshvink conducted such an experiment. Fragments of a meteorite from the Martian passage were taken, containing magnetized materials. They were heated, and it was found that at about 40 ° C, their magnetic orientation began to be lost. According to scientists, this indicates that all the way from Mars to Earth, our hypothetical ancestors were not heated above this point, far from the temperature at which thermophilic bacteria die.
How could this happen? Simulations undertaken after these experiments showed that if a large meteor or asteroid crashed into Mars, then it could immediately pierce the crust, without having time to initiate the process of explosive evaporation of the materials surrounding it. Since the second space velocity for Mars is three times lower than the Earth's, an underground explosion could lift the debris surrounding the impact site into space without strong heating or exposure to a powerful shock wave. By the way, the model showed that the material raised in this way could begin to flow to Earth just nine months after the asteroid hit Mars. It is unlikely that modern spacecraft on chemical rockets are capable of delivering astronauts there much faster than their ancestors could fly from there.
Perfectly! But how did they not overheat when they hit Earth? The secret could be … an ablative heat shield, Mr. Kirshvink believes. The outer layers of the meteorite melted when entering the atmosphere, and then they were carried away from the surface of the falling body in the form of drops, thereby reducing its heating. SpaceX ships protect themselves from overheating in a very similar way, so the method can be considered quite reliable and proven.
But this is all just speculation, isn't it? And Joseph Kirshvink, of course, will agree with you, noting that you need to look for evidence. Moreover, he believes that he has already partially found them. Many terrestrial creatures, from bacteria to mammals, have in their bodies magnetite, a substance from the class of iron oxides, biogenically formed by living organisms from iron. And there is a lot of this substance in them, up to 4% of the dry mass of Magnetospirillum bacteria, which are most likely the most primitive creatures that use magnetite for orientation in the Earth's magnetic field.
Kirschvink's team claims to have found magnetite - too pure to be abiogenic - in meteorites of Martian origin. Normally, magnetite contains inclusions from the environment in which it was formed, while meteorite magnetite has no such traces.
What is confusing about this evidence system? Older people probably remember the 1996 incident, when NASA specialists found carbon in the Martian meteorite ALH 84001, which is close to organic in isotopic composition - along with something that resembled bacteria, only extremely small, much smaller than 400-nanometer archaeobacteria (and these are the smallest living things on our planet). This was followed by years of pointless wrangling, which boiled down to the fact that the morphology of living beings cannot be a guide to action due to its innate debate (when it comes to such small objects) and that carbon, isotopically resembling that created by living organisms, under certain conditions can to form outside them.
The same fate may await Joseph Kirschvink's evidence, because magnetite is far from such a clear and unequivocal evidence as a living Martian organism. Finally, the scientist's assumption about biogenic magnetite on Mars implicitly implies that the common primordial ancestor (forefathers) of all living things was a creature capable of orienting along the lines of a magnetic field. And this, to put it mildly, is difficult to verify. And it is worth noting that most terrestrial bacteria, as far as science knows, do not have the ability to navigate by the magnetic field.
Noah's land is the region of Mars in which traces of water were first discovered on the Martian surface during the Noah era. Could the land of our bacterial ancestors have looked like this?
It is difficult to perceive the argument about magnetite as decisive also because the recently published work again raised the vague question of the mechanism by which a variety of living organisms produce magnetite from iron. It is still not very clear, and if so, then we will not dare say whether something like this can happen in inanimate nature and whether traces of magnetite in Martian meteorites are the result of abiogenic processes.
And yet it is worth recalling that the experiments of Mr. Kirschvink showed that if there was life on Mars, it could colonize the Earth in the shortest possible time, at least not slower than the current earthlings - Mars.
But in order to have complete confidence that this particular planet is our ancestral home, we need more serious evidence. Perhaps traces of that very early bacterial life on the Red Planet itself?