The origin of life is unclear, with many theories supporting different requirements for the conditions needed for life on earth now. However, the conditions for life now, are considerably different to the early Earth conditions of the Hadean Eon, which was unstable and hostile to life, and known as the Late Heavy Bombardment (Anon., 2022), a period of extreme heat due to constant collisions of planetesimals and meteorites.

At this moment in time, roughly 4 billion years ago, the earths surface was uninhabitable due to extreme heat from meteorites and magma beneath the Earths crust. Along with this, the surfaces exposure to ultraviolet radiation was too high, and therefore meant that life couldn’t have formed on the earths surface during this period. However, the deep ocean protected against this radiation, and was incredibly rich in minerals from sediment deposits and magma. Cracks in the sea floor, forming hydrothermal vents, released mineral rich magma, generated heat, and were responsible for the high pH (high alkalinity). This, along with the oceans high pressure, meant that organic molecules could exploit energy and minerals to form the building blocks of life. This is the theory we are going to discuss: the formation of life at deep sea hydrothermal vents.

Hydrothermal vent systems are chemically reactive environments that constitute suitable conditions to sustain prebiotic synthesis at seafloor spreading zones (Martin et al., 2008), the process by which amino acids and nucleotides form. This ability to create organic molecules, and in turn protocells (the simplest form of a cell), supports the theory, as there are clear links between the components and structure of our cells today, and the conditions and elements of the early Earth environment at deep sea trenches.

The composition of cells reflect the environment of their possible formation, one example being the compartmentalisation of cells due to the phospholipid bilayers. This is important as this is thought to have formed the protocell. The bilayer membrane forms around an aqueous solution, to create a vesicle, which is tightly bound together by fat molecules repelling the salt water, making it more stable, meanwhile the high alkalinity helps the vesicles to keep their electric charge (University College London., 2019). The salt and high pH therefore favour the formation of such basic forms of cells, which could further evolve. Further evidence for this theory includes the importance of iron, due to the iron rich oceans 3 billion years ago after the Hadean Eon. It is heavily involved in cellular functions, like transporting oxygen and breaking down sugars and nutrients for energy, which are all crucial to functioning cells. As well as this, iron and sulfur rich chimneys in the deep ocean have also been investigated in relation to the origin of life, showing evidence that they support RNA oligomerization reactions (Burcar, 2015), which is the formation of polypeptide chains to form proteins, which again, aid cell functions.

As stated above, there is compelling evidence for the influence of hydrothermal vents on the formation of cells, and this, along with the conditions needed to support life during that time, such as water, pressure, pH and temperature, all favour this theory. These hydrothermal vents created these desirable conditions, along with pores and cracks in the chimneys to create microenvironments which are able to host and preserve life (Ananthaswamy., 2002). It is also possible that convection currents from magma-generated heat could have circulated these minerals and simple forms of life, allowing for migration and evolution into more complex cell forms.

Therefore, to conclude, although there are many theories surrounding the origins of life, the most compelling theory appears to be the creation of basic organelles and simple cell structures at hydrothermal vents, as early as 4 billion years ago (Anon., 2022).

References

Ananthaswamy, A. (2002). Swirling hot water on the ocean floor may have given evolution a kick-start. New Scientist, 176(2367), pp. 15.

Anon. (2022). Wikipedia simple English. [online] available at: https://simple.wikipedia.org/wiki/origin_of_life

Burcar, B.T., Barge, L.M., Trail, D., Watson, E.B., Russell, M.J. & McGown, L.B. (2015). RNA Oligomerization in Laboratory Analogues of Alkaline Hydrothermal Vent Systems, Astrobiology, vol. 15, no. 7, pp. 509.

Clarkson University. (2017). Hydrothermal vent model.

Garlick, M. (2020). Late Heavy Bombardment. Available at: https://youtu.be/NafhLy22DJQ

Martin, W., Baross, J., Kelley, D., & Russell, M. J. (2008). Hydrothermal vents and the origin of life. Nature Reviews.Microbiology, 6(11), 805-14.

University College London. (2019). Deep sea vents had ideal conditions for origin of life. Science daily. Available at: https://www.sciencedaily.com/releases/2019/11/191104112437.htm