Biologist Mikhail Nikitin: how to prove that life on Earth arose by itself

Very soon Mikhail Nikitin will speak at the conference "Scientists against myths", which is organized by"ANTROPOGENESIS.RU». There, the biologist will talk about the "silicon aliens" that influenced the formation of our planet and the appearance of living organisms on it.

In this regard, we asked him to briefly tell our readers what view of the origin of life scientists hold and why other points of view are not so consistent.

What do scientists think about the origin of life on Earth?

First, let's define what life is. A strictly unambiguous definition, such as in mathematics, cannot, of course, be given. But the NASA expert commission, leading the search for life in the Universe, highlighted the following definition:

Life is a chemical system capable of Darwinian evolution.

"Chemical" means "consisting of atoms and molecules and using the reactions between them." And the ability for Darwinian evolution characterizes the presence of four necessary and sufficient conditions:

1. Reproduction.
2. Heredity (offspring are similar to parents).
3. Mutations (the offspring are still slightly different from the parents).
4. Selection (the probability of further reproduction depends on mutations).

Cell

Today, the cell is considered the smallest elementary unit of life. There are, of course, viruses that are much simpler, smaller, and also capable of Darwinian evolution. But they are all parasitic on cells, and in the wild they cannot be separated.

In this case, it is logical to assume that life originated with the advent of the cell. However, biologists there are big doubts about this.

RNA

It is now widely believed that once upon a time there were living organisms even simpler than cells.

According to this hypothesis, the most primitive life forms used only one of the existing types of biopolymers - the RNA molecule. For comparison: for the work of modern cells, they already need three: RNA, DNA and proteins.

But in the precellular era, all functions had to be performed only by RNA. She accelerated chemical reactions instead of proteins and acted as a repository of hereditary information instead of DNA.

So it was until some life forms mastered new technologies - the synthesis of proteins and DNA. Having done this, they became the cells that now make up all living things (except for viruses). And other forms could not compete with them and died out.

Chemical compounds

Before the RNA World planet Earth was not modern. Some scientists managed to simulate the conditions that were on it at that moment and trace the spontaneous generation of life.

One of the first such experiments was the Miller-Urey experiment, set up in the 1950s. Scientists took a mixture of gases - methane, ammonia and hydrogen - and drove them into a tricky glass installation. On one side she had a flask with heated water, on the other - a hole for steam to escape. Electrodes were soldered there, which let through discharges imitating lightning. The steam then entered the refrigerator, where it could condense.

A few weeks after the start of the experiment, scientists noticed that in the water under such conditions formed amino acids - building blocks of proteins - and some other molecules that make up living organisms.

This became a very important observation. However, now its meaning has been rethought. It is believed that the conditions that Miller and Urey reproduced are not similar to the earth, but to those that were in the protoplanetary cloud from which the solar system was formed. Because, as we later learned, the Earth never had an atmosphere of methane and ammonia.

By the way, the amino acids that were formed in the Miller apparatus are very similar to those that are actually found in some meteorites.

After this experience, other scientists also tried to simulate the formation of organic substances from carbon dioxide, which dominated the atmosphere of the ancient Earth and is now found in large quantities in atmosphere Mars and Venus.

They experimented with crystals of zinc sulfide, which, when irradiated with sunlight in water, restores carbon dioxide and converts it into formic, acetic, malic acids, and when nitrogen is added, into amino acids.

In addition, experiments were carried out to obtain the building blocks of DNA - nucleotides and nitrogenous bases. For example, Carl Sagan in the 1960s was able to obtain the latter from hydrocyanic acid, a substance that formed in the oxygen-free atmospheres of ancient Earth. Now hydrocyanic acid is also widely distributed in space - for example, in comets or on modern Titan, a satellite of Saturn.

Chemical elements

Those chemical elements, which uses earthly life, are among the most common in the universe. These are carbon, nitrogen, oxygen, hydrogen, magnesium, sulfur, iron.

In addition to them, other three elements that did not participate in the spontaneous generation of life on Earth are also considered common. These are helium and neon, which are not capable of chemical reactions, as well as silicon, which becomes active only at very high temperatures.

These chemical elements existed before the appearance of the Earth and the solar system. Their composition was formed by the first generation of stars due to thermonuclear reactions. So, immediately after the Big Bang, the Universe consisted only of hydrogen, helium and lithium, and only then did heavier elements appear.

They interacted with each other in a random order and led to the formation of chemical compounds, among which were amino acids and nitrogenous bases, which we mentioned above.

Spontaneous generation of life

In the process of the origin of the living from the inanimate, chance and regularity were certainly combined. Biological evolution only works when there are both mutations and natural selection. Life, most likely, also spontaneously originated based on this principle.

Most likely, there was some kind of natural selection before the advent of reproduction. For example, nitrogenous bases in RNA and DNA, such as adenine, cytosine, guanine, and uracil, stand out from other related molecules due to their high resistance to ultraviolet radiation.

Then they were randomly combined into RNA chains. And the one that could increase the likelihood of their own copying began reproduction, natural selection and Darwinian evolution. And then the natural complication towards the cells began.

Why Aliens or God Couldn't Create Life

If life did not originate by itself, then either civilizations could help it in this alienswho arrived on Earth, or some supernatural beings. For example, God. Let's explore these theories in more detail.

aliens

It has been proven that the Big Bang happened about 13.5 billion years ago. The age of terrestrial life is quite solid compared to the age of the universe. The evolution from microbes to sentient beings, Homo sapiens, took approximately 4 billion years.

It would probably take the aliens about the same amount of time. And they could hardly get ahead of us. After all, after the Big Bang, the accumulation of elements heavier than helium - carbon, hydrogen, iron - did not happen instantly. The stars have been synthesizing them for billions of years. That is, within the Galaxy, the conditions for the emergence of planetary systems on which life is possible did not develop immediately, and the aliens would hardly have time to become space civilization before us.

But even if they somehow succeeded in doing this, then a natural question arises: how did their life arise? If it is itself, then why do we not consider this possibility in relation to life on Earth?

God

Since we have no direct evidence of what God can and cannot do, it is, of course, much more difficult to find arguments here. Creationists will always be able to come up with an option for which they will not work, because "the ways of the Lord are inscrutable."

But personally, for example, I am convinced by aesthetic considerations. God is described as a superintelligent being. However, at the same time, there are many details in the device of living organisms that could not be made by any sane designer.

Only a fool would admit, for example, the presence of a recurrent laryngeal nerve in mammals.

It goes from the brain to the muscles of the larynx and at the same time makes a loop, descending first to the heart, bypassing the aortic arch and rising back. As a result, for the normal functioning of a giraffe, for example, you need 5 extra meters of nerve fiber. And at the same time, he will also suffer from a delay in the signal transit time.

It is clear that if animals were created by a rational being, it would not have committed such stupidity. Such a structure is much more like the result of the evolution of mammals from their fish-like ancestors. Those did not have a neck, the heart was located close to the head, and the outflow of blood from the heart was carried out thanks to several pairs of gill vessels. Therefore, tracing of the nerve around them seemed normal and did not pose a problem. And then the fish came to land, lost their gills, and some of their descendants had a thin, long neck. The further, the more this design began to interfere, but they could no longer refuse it.

Some creationists are promoting another idea: God only set off the Big Bang, and then did not touch universe. In the 17th-19th centuries, many scientists thought so too. For example, when Napoleon asked Laplace: “Where is God in your theories?” - the astronomer replied: "I do not need this hypothesis."

But even if the Lord really did not interfere in anything after the Big Bang, then why does this contradict the idea of ​​evolution? How is this version of creationism fundamentally different from scientific pictures of the world?

Why is life not forming on other planets now?

Earth-like planets with a solid stone surface, which are not found on the gas giants Jupiter and Saturn, in solar system four: Earth, Venus, Mercury and Mars.

Both now and before, it was too hot on Venus: it is 450 ° C there, and in such conditions lead easily melts. At such high temperatures, even the most extremophilic microbes do not survive, and proteins, RNA and DNA are destroyed very quickly.

Mercury is very hot during the day - up to 400 ° C, and cold at night - up to -170 ° C. There is no atmosphere and no water.

Modern Mars is also not very hospitable: it is cold there, like in Norilsk, and dry, like in the Namib Desert, plus radiation. However, there are enough traces on this planet that in ancient times there was liquid water, a denser atmosphere and higher temperatures, quite livable.

The fact is that all terrestrial-type planets were formed by the collision of smaller objects - planetary embryos. At these moments, a lot of heat was released, due to which their surfaces were very hot. The Earth also passed through a stage of an ocean of magma, after which it then cooled for a long time - perhaps up to 300 million years.

Since Mars is smaller, its collisions with planetary germs were not as energetic, and it cooled faster.

The bottom line is that it could have had habitable conditions 100-200 million years earlier than our planet. But there is no direct evidence for this.

It is possible that we are Martians. After all, first living forms could appear there, and then fly to Earth with meteorites.

Now, when Mars is dry and cold, there is either no life left there at all, or it hides very well somewhere in its depths, under the surface. One of the proofs of this can be methane impurities periodically appearing in the atmosphere - this is a gas that quickly breaks down in the atmosphere. If it was found, then there must be some kind of active source on the planet - for example, methanogenic microbes.

How can you speed them up? evolution? To do this, you need to drop some kind of icy body with a diameter of about 500 km from Mars onto Mars. Kuiper belts. Enough water would get there to form an ocean, and the energy from such an impact would possibly warm up the planet and spur its already frozen geological activity. But it is clear that the probability of this is negligible.

If we want to make Mars habitable, then we need to take matters into our own hands and deliver water there in the form of smaller ice cubes, and then artificially restore a magnetic field on the planet - without it, it will be poorly protected from cosmic rays and will retain a high level of radiation for surfaces.

This is just what it sounds like too fantastic.