Life on Earth began three billion years ago. Since then, evolution has transformed elementary, single-celled organisms into the variety of shapes, colors, sizes, and functions that we see today. But how exactly did life arise in the primordial broth - water contained in shallow springs and saturated with amino acids and nucleotides?
There are many theoretical answers to the question of what exactly caused the origin of life, from a lightning strike to a cosmic body. Here are just a few of them.
Spark of electricity
That very metaphorical spark of life could be a completely literal spark or many sparks, the source of which was lightning. Electric sparks entering the water could cause amino acids and glucose to form, converting them from an atmosphere rich in methane, water, hydrogen and ammonia. This theory was even confirmed experimentally in 1953, proving that lightning could well be the cause of the formation of the basic elements necessary for the emergence of the first forms of life.
After conducting the experiment, scientists were able to prove that the early atmosphere of our planet could not contain enough hydrogen, but the volcanic clouds covering the Earth's surface could include all the necessary elements and, accordingly, enough electrons to cause lightning.
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Underwater hydrothermal vents
Relatively strong deep-sea vents could become a necessary source of hydrogen for the formation of the first living organisms on their rocky surfaces. Even today, a wide variety of ecosystems are developing around hydrothermal vents, even at great depths.
Clay
The first organic molecules could be found on a clay surface. Clay always contains a sufficient amount of organic components, in addition, it could become a kind of organizer of these components into more complex and effective structures similar to DNA.
In fact, DNA is a kind of a map for amino acids, indicating exactly how they should be organized in the cells of complex fats. A group of biologists from the University of Glasgow in Scotland argue that clay could be such a map for the simplest polymers and fats, until they learned to "self-organize."
Panspermia
This theory makes one think about the possibility of a cosmic origin of life. That is, according to her postulates, life did not originate on Earth, but was just brought here with the help of a meteorite, for example, from Mars. There were enough fragments found on the ground, which supposedly came to us from the red planet. Another way of "space taxi" for unknown life forms are comets, which are able to travel between star systems.
Even if this is true, panspermia is still not able to answer the question of how exactly life originated from where it was brought to planet Earth.
Under the ice sheet
It is possible that the oceans and continents three billion years ago were covered with a thick layer of ice, because the sun was not as bright as it is today. Ice could become a protective layer for fragile organic molecules, preventing ultraviolet rays and cosmic bodies colliding with the surface from harming early and weak life forms. In addition, the lower temperature could have caused the evolution of the first molecules into stronger and more durable ones.
RNA world
The theory of the RNA world is based on the philosophical question of the egg and chicken. The fact is that for the formation (duplication) of DNA, proteins are needed, and proteins cannot self-replicate without the very map embedded in the DNA. So how did life arise if one cannot appear without the other, but both exist beautifully in the present? The answer may be RNA - ribonucleic acid, which is capable of storing information like DNA and serving as protein enzymes. More perfect DNA was formed on the basis of RNA, then more efficient proteins completely replaced RNA.
Today RNA exists and performs several functions in complex organisms, for example, it is responsible for the work of certain genes. This theory is quite logical, but it does not answer the question of what was the catalyst for the formation of ribonucleic acid itself. The assumption that it could have appeared by itself is rejected by most scientists. The theoretical explanation is the formation of the simplest acids PNA and TNK, which then developed into RNA.
Simplest start
This theory is called holobiosis and comes from the idea that life began not from complex RNA molecules and the primary genetic code, but from the simplest particles interacting with each other for the sake of metabolism. Perhaps these particles eventually developed a protective shell, like a membrane, and then evolved into one, more complex, organism. This model is called the "enzyme model of metabolism", while the theory of the world of RNA is called the "model of the primary genetic code."