If you asked a professional in the 1970s - a biologist, archaeologist, or geologist - how old life on Earth was, you would get a very cautious “I don’t know” answer. We know that the Earth was inhabited even before the appearance of mammals, birds, dinosaurs, reptiles, fish, crustaceans and even sea stars and jellyfish - before the Cambrian explosion, which happened 500-600 million years ago. We know that she was a living planet, but we have incredibly little evidence of this. Despite the fact that a very impressive fossil record has accumulated over half a billion years, the very process of fossil formation imposes certain restrictions on our ability to look back into the past. Usually the bodies of animals are covered with water, and on top - with soil sediments, and this is how fossils are formed that we can study. Indeed, otherwise the Earth would be strewn with the corpses of dead creatures and reptiles.
But there is sedimentary rock in which the fossils are stored. However, if you place too many layers on top of your fossils, the combination of pressure and time will lead to changes in these rocks, and therefore in their contents. In a rock that begins to change, fossils will remain only if the rock is partially changed. There will be nothing left in completely transformed rocks. Therefore, if you asked a scientist who studies the natural history of the Earth, 40 years ago, how old life on Earth is, he would tell you that one or two billion years is already accurate, but maybe more - but it will not be possible to prove.
After all, we cannot just go back in time and find out what was then; the only thing we have left from those times are tiny pieces of fossil. The land has changed a lot since then. If three billion years ago, giant lampposts that use cellular communications roamed our planet, we might never know about it.
And yet, since the 1970s, we have learned something: even if the fossils themselves are no longer there, if they are no longer disassembled, not distinguished, the remains of organic matter leave a special signature in the form of carbon. This "carbon dating" can be used to measure the ratio of carbon-14 to carbon-12 in organisms, as both forms of carbon are absorbed by organic matter, and carbon-14 is generated in the upper atmosphere by cosmic rays and decays at about 5,700 years. As long as you live, you breathe in and breathe in both forms of carbon; when you decompose, carbon-14 decays and is not replaced by new carbon-14. Therefore, if you could measure the ratio of carbon-14 to carbon-12, you could figure out - roughly, within a few thousand years - how long ago that particular organism died.
Radiocarbon dating allows us to go back in time several hundred thousand years or so before carbon-14 becomes too low to be effective. But there is another form of carbon that we have not yet mentioned, and all in the same breath of air: carbon-13, which, like carbon-12, is stable and which contains about 1.1% of other forms of carbon.
Living organisms - as far as we can find out - prefer carbon-12 over carbon-13 because metabolic enzymes react with the former more efficiently. If you find an ancient source of carbon that is rich in carbon-12, not -13, that's good evidence that this is the remains of an ancient life form. By studying graphite, a form of pure carbon deposited in highly metamorphosed rocks (zircon), we were able to look much deeper than the 1-2 billion year barrier and displaced the emergence of life on Earth to a point 3.8 billion years ago - that is, after just 750 million years after the formation of the Earth. But in 2015, we surpassed ourselves.
Promotional video:
Having discovered deposits of graphite in zircons that are 4.1 billion years old, especially rich in carbon-12, we now have solid evidence that life on Earth has accompanied the planet for 90% of its history, and perhaps longer. In the end, if you find the remains of organic matter in a certain place, it means that organic matter will be at least as old as the place of its burial, and maybe even older. So much older that one would think that the Earth came with life.
Perhaps it was.
There is a hypothesis known as the panspermia hypothesis, and as long as there are authority figures behind it, it will be somewhat authoritative. You see, Earth was born after over nine billion years of cosmic evolution. The filling, which later formed the basis of our planet, before that was other generations of stars that became planetary nebulae, supernova remnants and even neutron stars, generously endowing our Universe with heavy elements.
In many cases, these heavy elements have been linked together in extremely interesting molecular chains that we today regard as "truly organic matter."
When meteorites, like the Murchison meteorite, hit the Earth, we can analyze what they have inside. We find all kinds of interesting organic molecules, but the most interesting thing about them is the amino acids. Despite the fact that about 20 amino acids play an important role in the processes of life on Earth, we found about 100 unique amino acids in this meteorite. Obviously, the ingredients of life are abundant throughout the universe. We even found amino acids on the Moon, which indicates that whoever brought amino acids to Earth, this happened before the formation of the Moon, less than 100 million years after the formation of the solar system.
And if all the ingredients are in place, maybe some primitive life form should be present for everyone? If all life on Earth has a universal common ancestor, could there be many forms of ultra-primitive life in the Universe, one of which best adapted to the environment of the young Earth, survived, flourished, evolved, and surpassed others? We don't have enough evidence to favor this hypothesis over others, but if we keep pushing the threshold further and further: 4.3 billion years ago, 4.4 billion, 4.45 billion … we have no choice but to conclude, that the Earth was born "alive" in a sense.
Perhaps the geysers of Enceladus, the black smokers on Neptune's moon Triton, or even the snowy ridges of Pluto contain these primitive life forms, and that it was the bombardment of comets and other Kuiper belt objects that brought these primitive life forms to us. The best thing about this theory is that we can test it if we decide to send a mission to these worlds.
ILYA KHEL