The primordial soup or broth is a hypothetical mixture of substances and conditions that occurred in the atmosphere and terrestrial surface before life appeared on the planet and that allowed its development from inert materials. It is one of the most plausible scientific theories about the origin of life on Earth, although there still seems to be a long way to go to know exactly how life arises from its non-existence.
primordial soup theory
According to the primordial soup theory, the process of abiogenesis that took place on Earth billions of years ago would be explained by physical and chemical reactions that gave rise to the first organic compounds from inorganic compounds. These first organic compounds, even considered inert or non-living, accumulated in the first oceans and bodies of water, forming the so-called primordial "soup" or "broth"also called prebiotic, primitive, primordial or nutritious soup.
In the primordial soup, simple organic molecules reacted with each other to form increasingly complex molecules, including nucleic acids and proteinsconsidered the two types of fundamental substances in the different structural and functional components of all terrestrial living organisms.
These molecules would begin to add at some point until forming what would be the first form of life, capable of preserving and self-replicating. This process would have begun between an age of 4,410 million years, when the first seas and oceans were formed, and between 4,280 and 3,770 million years, the date from which the oldest known signs of life date.
Darwin already intuited this theory in 1871 when he spoke of the «warm little pond» (warm little pond) in a letter written to his friend Joseph Dalton Hooker. But the first primordial soup theory is attributed to the Soviet biochemist Alexander Oparin in 1924. The same idea was elaborated by the English scientist John Sanderson Haldane in 1929 independently. Hence the primordial soup theory is also known as the Oparin–Haldane hypothesiswhose main postulates are:
- The original atmosphere was reducing.
- This atmosphere was subjected to various forms of energy, such as high temperatures and strong electrical dischargeswhich promoted the formation of simple organic compounds or monomers.
- These simple compounds are accumulated in a "soup" in the first seas and oceansprobably with a higher concentration in certain areas, for example along coastlines, beaches, winds, etc.
- Simple organic compounds combine with each other to form polymers more complex from which life arose.
Conditions and composition of the primordial soup
Conditions on Earth in its early years were very different from what they are now. The atmosphere hardly contained oxygen, on the contrary, it was a strongly reducing atmosphere full of hydrogen, methane, ammonia and water vapor.
When the temperature dropped enough to allow the water to remain stable in a liquid state, these substances were carried by the rain to the seas and oceans, where they would combine to form amino acids and other organic substances that would eventually give rise to life. hundreds of millions of years later.
For these first organic molecules to form, the presence of some kind of catalyst was necessary. Some research suggests that the main catalysts were heat and electrical discharges, which were very abundant in the atmosphere of that era.
The first experimental demonstration that this theory could be valid is the experiment of Stanley Miller and his professor Harold Urey, made in 1953. They mixed water and various highly reducing gases: methane, ammonia and hydrogen. They applied electric shocks and in about a week they had formed amino acids.
The next important experiment to support the primordial soup theory was carried out by Joan Oró in 1961. The formation of adeninea purine base that is part of nucleic acids, from an aqueous mixture of ammonium cyanide.
However, these experiments do not show that this was what happened for life to arise, since the conditions applied in the laboratory certainly have nothing to do with the real conditions that occurred on Earth. What these experiments demonstrate is the possibility, and also the ease, of forming organic molecules common in living organisms from inorganic substances.
These first organic substances could have accumulated in hydrophobic or oily films on beaches and sandbanks, where they would form increasingly complex molecules until the first molecules with some biochemical function appeared. At some point these molecules acquired the ability to self-replicate until the first form of life appeared in this primordial soup.
Evolution and natural selection would do the rest to generate all the diversity of life on the planet, including of course the human species and our ancestors.