The Primordial Soup Hypothesis: how did life on Earth emerge?

Long before the existence of the scientific methods we have today, mankind went looking for answers on how we came to be. Nowadays we have many different creation myths that possibly tell us the story of how everything came into existence. Several types of myths exist, for instance, in which gods create humans (e.g. Kukulkan), life emerges from nothing (e.g. Sumerian creation myths), or myths in which the world or universe starts out in a state of chaos (e.g. Pangu). But instead I will focus on abiogenesis, the course of how life can emerge from non-living particles.

Building blocks of life
A theory that fits the concept of abiogenesis is the primordial soup hypothesis. This proposition was initially put forward by Oparin and Haldane, who were inspired by experiments conducted by Miller and Urey. In their experiments they had tried to simulate a setting similar to early Earth, where organic compounds were able to form in a spontaneous manner. And this is what Oparin and Haldane postulate in terms of the emergence of life on Earth. Amino acids are often referred to as the building blocks of life, several are necessary for us to consume, as the body cannot create these by itself. At present we have identified about 500 different amino acids (Wagner & Musso, 1983). According to the primordial soup hypothesis, these amino acids formed from gases in the atmosphere and piled up in the ocean. Afterward, through chemical processes these building blocks turned into macromolecules, such as proteins. And importantly, these macromolecules were self-replicating (McNihol, 2008).

RNA, the essential macromolecule for all life
RNA, an abbreviation for ribonucleic acid, is a macromolecule that plays a big role in many biological processes in all forms of life. And the birth of RNA was an important factor in the formation of new life forms. RNA is responsible for, among other things,  carrying genetic instructions from DNA to parts of our cells that synthesize proteins. It also plays an important role in copying DNA in our bodies (Joyce, 1993).

Protocells in the primordial soup
The primordial soup refers to the primeval ocean in which the organic compounds came into existence through chemical processes.  In order for these processes to take place, sources of energy where needed. These were likely to be: radioactive decay, UV radiation, electrical discharges from the atmosphere, planetesimal impacts, and thermal energy from volcanism (Corliss, Baross, & Hoffman, 1981). These energy sources were imperative in terms of forming protocells. These first types of cells did not contain any organelles. Organelles are often described as the organs of a cell, these include structures such as ribosomes, mitochondria, nuclei, endoplasmic reticulum, etc. These structures carry out tasks that are important in a cell’s life. A theory on how modern day cells ended up with these organelles might be explained through endosymbiosis.

Endosymbiosis
Symbiosis is a common term in biology in regards to animals. A well-known example of this is clown fish and sea anemones. Both species protect each other from predators. Clown fish hang around sea anemones and scare off its natural predator, while clown fish do this to hide from their own predators. I would like to point out that this relationship isn’t necessarily intentional, the clown fish isn’t consciously protecting the anemones. This same principle can be applied to the evolution of cells. Because of organelles, such as the mitochondria taking symbiotic residency in its host cell (Kutschera & Niklas, 2005).

Beginning of life
And from here on single-cell organism life is present on Earth, this is where the evolution of life really begins. Different types of cells were formed: eukaryotic vs prokaryotic cells. Eukaryotic cells have a nucleus that carries its DNA, while prokaryotic cells do not have such a nucleus. A prokaryote is a single-cell organism, which are either classified as bacteria (e.g. E. Coli) or archaea (halophiles). Most of the other organisms have eukaryotic cells, such as humans. The earliest life forms are estimated to have emerged 3.5 billion years ago, as organic matter estimated from this time period, has been found (Allwood, Walter, & Marshall, 2006). Mondern day humans evolved from the Homo Erectus 200,000 years ago (Bradshaw, 1997). Life is still evolving and will continue to do so until the end up times.

Allwood, A. C., Walter, M. R., & Marshall, C. P. (2006). Raman spectroscopy reveals thermal palaeoenvironments of c. 3.5 billion-year-old organic matter. Vibrational Spectroscopy, 41(2), 190-197.

Bradshaw, John L. (1997). Human Evolution: A Neuropsychological Perspective. Psychology Press.

Corliss, J. B., Baross, J. A., & Hoffman, S. E. (1981). A Hypothesis Concerning the Relationships Between Submarine Hot Springs and the Origin of Life on Earth. Oceanologica Acta, Special issue.

Joyce, G. F. (1993). The RNA world: Life before DNA and protein.

Kutschera, U., & Niklas, K. J. (2005). Endosymbiosis, cell evolution, and speciation. Theory in Biosciences, 124(1), 1-24.

McNichol, J. (2008). Primordial soup, fool’s gold, and spontaneous generation. Biochemistry and Molecular Biology Education, 36(4), 255-261.

Wagner, I., & Musso, H. (1983). New naturally occurring amino acids. Angewandte Chemie International Edition in English, 22(11), 816-828.

Amino acids / protein schematic source.

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