If we try to take the common part from these definitions, it turns out that living things exchange substances with the environment (metabolism), have the ability to grow, react to external conditions, reproduce... Let's check these provisions.

Metabolism. This is a property of almost any chemical process. The same candle flame, for example, takes oxygen from the environment and gives off carbon dioxide, just like us. Does this make it alive?

Reproduction. A computer virus reproduces too.

Growth. Crystals also grow. And by knocking over the same candle, you can accidentally "grow" a fire throughout the entire room.

Reaction to external conditions. Ice crystals grow faster at low temperatures - they react to external conditions.

This means that all these signs - metabolism, the ability to reproduce and grow, reaction to the external environment - are not enough.

Scientists have added a new condition to the definition of life: a living being creates more complex substances in the process of metabolism.

A crystal grows, a computer virus reproduces, fire creates complex substances. But this is not life!

On the one hand, the condition is correct: all the multitude of living proteins (and there are millions of different ones) are created from twenty-odd amino acids. On the other hand, in the same candle flame, very complex substances are created randomly: anthracene, phenanthrene... There is, however, a fundamental difference.

What is synthesized in the flame is not needed by the fire, it is even harmful (for example, it goes out from soot). But what is synthesized in a living organism goes to its construction, to help in the same synthesis, to protect from the external environment. It remains, and then can pass on to descendants.

This condition, which was called "accumulation and transmission of information", is now considered the main property of life. And how this information is accumulated - by the synthesis of substances necessary for survival, the transmission of antibodies, innate instincts or the printed word (as is happening to you now) - this is already secondary.

How could the inanimate become alive?
How did life originate? There are also many answers to this question. "Brought from space", "planted as an experiment by some civilization" - such answers only raise the same questions again: how did life then arise on the home planet of this civilization?

Observing the living world around us, it is very difficult to imagine that all this complexity and diversity could somehow arise on their own. And if we assume that in some ancient times all living things were represented by only one type of life?

Now geologists find many layered stones, stromatolites, which are formed by long-term colonies of cyanobacteria. So, the oldest of these stones are three and a half billion years old. No other traces of the activity of living beings of that time are known. That is, it seems that the only ones who lived on Earth then were cyanobacteria.

Stromatolites But even a bacterium is already a very complex organism. It synthesizes many different proteins, hereditary information is stored in DNA, and RNA (ribonucleic acid) is used for transmission and transport. Could it be that all these substances suddenly arose and came together by chance?
Cyanobacteria
Scientists have recently discovered that there are biochemical reactions that do not require protein. These reactions can occur with the participation of only RNA, the so-called ribozymes.

Let's imagine such a living organism. It most closely resembles a drop with a solution of nucleic acids inside. Some molecules store hereditary information, while others synthesize new RNA. Still others form a shell.

How does nutrition and reproduction occur in such an organism? Suitable molecules from the external environment form a pair with the molecules of the shell and are drawn in. Inside, they also form pairs with existing "long" RNA chains. Naturally, for a new chain to be linked by chemical bonds, a lot of time is needed, or a short-term high temperature, or the help of another RNA ribozyme.

RNA molecule under an electron microscope
But the main task is more or less fulfilled - such a drop of solution can already accumulate and transmit useful information, that is, it is already alive.

What makes suitable molecules unite?

A coincidence?