Ask Ethan: How fast could life appear in the universe?

Organic molecules are found in star formation regions, in star residues and in interstellar gas, throughout the Milky Way. In principle, the ingredients of rocky planets and life on them could appear in our Universe quickly enough, and long before the appearance of the Earth.

The story of how the universe has become what we see it today, from the Big Bang to the vast space filled with clusters, galaxies, stars, planets and life, unites us all. From the point of view of the inhabitants of the planet Earth, before the moment of the appearance of the Sun and the Earth, 2/3 of the space history passed. However, life appeared on our world as long as we are able to look into the past with the help of measurements - perhaps even 4.4 billion years ago. It makes you wonder: has life appeared in the Universe before our planet, and in principle, how long could it have appeared? Our reader wants to know:

How soon after the Big Bang could there be enough heavy elements to form planets, and possibly life?

And even if we confine ourselves to the type of life that we consider “similar to ours,” the answer to this question will send us further into the past than you could imagine.


Graphite deposits found in zircon are the oldest evidence of carbon based life on Earth. These deposits and the amount of carbon-12 in them date the appearance of life on Earth for more than 4 billion years ago.

Of course, we cannot go to the very beginning of the Universe. After the Big Bang, there were not only stars or galaxies, there were not even atoms. Everything needs time to appear, and the Universe, containing after the birth of a sea of ​​matter, antimatter and radiation, began its existence from a fairly homogeneous state. The densest regions were by a small fraction of a percent — perhaps only 0.003% — denser than the average. This means that it will take a huge amount of time to work on a gravitational collapse to create, for example, a planet that is 10–30 times denser than the average density of the Universe. And yet, the universe had as much time as necessary for the appearance of all this.


Standard time line of the history of the universe. Although Earth appeared only after 9.2 billion years after the Big Bang, many steps necessary to create a world like ours took place quite early.

After the first second, antimatter annihilated with most of the matter, and few protons, neutrons and electrons remained in the sea of ​​neutrinos and photons. After 3-4 minutes, protons and neutrons formed neutral atomic nuclei, but almost all of these were isotopes of hydrogen and helium. And only when the Universe cooled to a certain temperature, which took 380,000 years, could the electrons join these nuclei and form neutral atoms for the first time. And even with these fundamental ingredients, life - and even rocky planets - was still impossible. Hydrogen and helium atoms alone are indispensable.


With the cooling of the universe, atomic nuclei appear, and after them, with further cooling, neutral atoms. However, almost all these atoms are hydrogen and helium, and only after many millions of years ago stars begin to form, in which heavy elements appear that are necessary for the appearance of rocky planets and life.

But gravitational collapse is a reality, and, having enough time, it will change the look of the Universe. Although at first he goes for a very long time, he continues tirelessly and is gaining momentum. The denser the region of space becomes, the better it gets to attract more and more matter. Plots starting with the highest density grow faster than others, and our simulations show that the very first stars should have formed approximately 50-100 years after the Big Bang. These stars were supposed to consist exclusively of hydrogen and helium, and could grow to quite large masses: hundreds or even thousands of solar. And when such a massive star is formed, it will die in one or two million years.


But at the time of the death of such stars, something amazing happens - and all thanks to their lives. All stars synthesize helium from hydrogen in the nucleus, but the most massive ones not only synthesize carbon from helium - they transfer to the synthesis of oxygen from carbon, neon / magnesium / silicon / sulfur from oxygen, and further and further along the periodic table of elements until they reach iron, nickel and cobalt. After that, there is nowhere to go, and the core collapses, triggering a supernova explosion. These explosions eject huge amounts of heavy elements into the Universe, creating new generations of stars and enriching interstellar space. Suddenly, heavy elements, including the ingredients necessary for the emergence of rocky planets and organic molecules, fill these protogalaxies.


Atoms bind to form molecules, including organic molecules and biological processes, both on the planets and in interstellar space. As soon as the necessary heavy elements become available in the Universe, the formation of these “seeds of life” is inevitable

The more stars live, burn and die, the more enriched will be the next generation of stars. Many supernovae create neutron stars, and the greatest number of the heaviest elements of the periodic table appear in neutron star mergers. An increase in the proportion of heavy elements means an increase in the number of rocky planets with greater density, the number of elements necessary for life we ​​know, and the likelihood of complex organic molecules. We do not need the average star system of the Universe to resemble the Solar system; we just need only to have several generations of stars live and die in the densest region of space in order to reproduce the conditions suitable for the emergence of rocky planets and organic molecules.


In the center of the remnants of the supernova RCW 103 there is a slowly rotating neutron star, which was previously a massive star that has reached the end of its life. And although supernovae are able to send heavy elements synthesized in the nucleus back to the Universe, it is the subsequent mergers of neutron stars that create most of the heaviest elements.

By the time when the universe was only a billion years old, the most distant objects, the abundance of heavy elements in which we can measure, contain a lot of carbon : as much as our Solar System has. A sufficient number of other heavy elements is being gathered even faster; Carbon may need more time to reach a high concentration because it mainly appears in stars that do not turn into supernovae, and not in those ultramassive stars that explode. Rocky planets don't need carbon; other heavy elements will come down. (And many supernovae create phosphorus ; no need to believe the recent reports, which are completely wrong exaggerate its deficit). It is likely that only a few hundred million years after the ignition of the first stars — by the time the Universe was 300 to 500 million years old — rocky planets had already formed around the most enriched stars.


Protoplanetary disk around a young star, HL Taurus ; Photo ALMA . The gaps in the disk indicate the presence of new planets. As soon as the disk has enough heavy elements, rocky planets can appear in it.

If carbon were not necessary for life, at the same time, in some regions of space, life processes could start. But for a life like ours, carbon is needed, which means that for a good probability of life, you will have to wait a little longer. Although carbon atoms will fall, it will take 1–1.5 billion years to recruit a sufficient amount of it: until the Universe knocks 10% of its current age, and not just 3-4%, required only for the appearance of rocky planets It is interesting to think that the Universe formed planets and all the necessary ingredients in the right quantity for the emergence of life, except carbon, and that in order to create a sufficient amount of the most important ingredient in life, you need to wait until the most massive of sun-like stars live and die.


Supernova remnants (left) and planetary nebula (right) - both of these methods allow stars to return burnt heavy elements back to interstellar space and use them to create stars and next-generation planets. Sun-like stars, after the death of which the planetary nebula remains, are the main source of carbon in the universe. It takes more time to produce it, because the stars, after the death of which a planetary nebula appears, live longer than those that die in the form of supernovae.

Extrapolation into the past of the most advanced forms of life on Earth that have appeared in different eras is an interesting exercise. It turns out that an increase in the complexity of genomes is subject to a certain trend. If you go back to a separate paired grounds , you get a period more similar to 9-10 billion years than 12-13 billion years ago. Is this an indication that life on Earth appeared much earlier than the Earth itself? And is it an indicator that life could start billions of years ago, and in our part of the cosmos it took several additional billions of years to start?


On this semi-log plot, the complexity of the organisms, measured by the length of functional non-redundant DNA in relation to the genome, which is calculated by the paired bases of nucleotides, increases linearly with time. Time is counting back in billions of years from the current moment.

At the moment we do not know. But we do not know where the line between life and not life passes. We also do not know whether earthly life began here, on a previously formed planet, or somewhere in the depths of interstellar space, without any planets at all .


Many amino acids that are not found in nature were discovered in the Murchison meteorite , which fell to Earth in Australia in 1969. The fact that there are more than 80 unique types of amino acids in a simple cosmic stone may indicate that the ingredients for life, or even life itself, did not appear on the planet at all.

It is very interesting that the raw, elementary ingredients necessary for life appeared shortly after the formation of the first stars, and the most important ingredient - carbon, the fourth most common element in the Universe - is the last ingredient to reach the quantity we need. Rocky planets in some places appeared much earlier than life could have appeared: just half a billion years after the Big Bang, or even earlier. But as soon as we have enough carbon, in 1–1.5 billion years after the Big Bang, all the steps necessary for the emergence of organic molecules and the beginning of movement towards life become inevitable. Whatever life processes that led to the emergence of mankind, no matter how much we understand them, they could begin their journey even when the Universe was ten times smaller than it is now.