It is estimated that planet Earth has existed for 4550 million years. Life as we know it, on the other hand, seems to have emerged about a billion years later. But where exactly does it come from? This question has been asked by philosophers and scientists for many centuries and has given rise to various theories about its origins.

In Western culture, such theories have their foundation either in Christianity or in science. In this sense, the proposals range from the will of a divine being to the evolution of our genetic material, including interventions of cosmic material and the composition of inert matter. In this article we will review 10 of the main theories about the origin of life on Earth .

10 theories about the origin of life

As we have said, the theories about the origins of life on earth range from the proposals of Christianity to the most complex scientific hypotheses; largely developed by the physical, chemical and biological sciences. We present below a tour of these proposals.

1. Theory of Creationism

The most widespread biblical account of the origins of life suggests that it occurred through the intervention and will of a divine being. In the book of Genesis, within the Old Testament, it is explained that this being was dedicated to generating the different states and living beings as we know them. In the course of seven days, he created the sky and the earth, and then he originated the light, the darkness, the seas, the vegetation, the sun and the moon, the animals; the man and the woman; and finally, he rested.

This is the theory that has been most valid in Western societies throughout the centuries , until the progress in research inherited from the Scientific Revolution questioned it.

2. Genesis theory under the ice

One of the proposals about the origins of life on earth is that billions of years ago, the oceans were completely covered by a very thick layer of ice. As this layer was so thick, even half a hundred meters, it was possible that organic compounds were very well protected from external agents, and from the sun itself, which was much more powerful given the conditions of planet earth.

Thus, the strong protection of the ice sheet could generate a safe interaction of microorganisms , and finally create life forms.

3. Theory of electrical activity

Broadly speaking, this theory proposes that electrical currents can produce simple amino acids and sugars, from different chemical compounds that are also simple and found in the atmosphere. In this sense, life would be originated as consequence of the presence of a ray that, when coming into contact with the elements of the Earth’s atmosphere, may have been responsible for originating the first and most basic forms of life.

4. Panspermia

Panspermia proposes that life on earth began from rocks, meteorites and remains of cosmic material that have impacted our planet since its first moments of existence. Such material is supposed to be transported through cosmic dust, and kept on earth by the action of gravity. The panspermia proposes that the existence of these remains could generate the organic and bacterial material necessary to generate life . It was first proposed by the German biologist Hermann Ritcher in 1865.

5. Spontaneous generation

Spontaneous generation is one of the oldest and best known theories about the origins of life. It proposes that life is generated spontaneously or naturally from microorganisms present in inert matter. In its oldest forms, the theory of spontaneous generation considered that life is created because some inert materials can give rise to living organisms (for example, manure generates flies).

In this context, the experiment carried out by the Italian doctor Francesco Redi, who was trying to prove that inert matter does not generate life, but rather attracts it, is classic. What he did was to leave a piece of meat uncovered, and another piece of meat inside a closed jar. He proved that flies did not emerge from the meat, but from the eggs left by other flies when the meat was uncovered. Finally, it was Louis Pasteur who proved that microorganisms do not arise from inert matter but are in the air, and this matter only attracts them.

6. Theory of abiogenesis

Reformulating the theory of spontaneous generation, the theory of abiogenesis has emerged, which proposes that there is a natural process in inert matter from which life emerges. For example, it is proposed that life on earth began when water vapor could finally condense, because this generated geochemical and astronomical processes that in turn originated the minimal genome. From this it follows that spontaneous generation could indeed be a real process, but millions of years ago (not in the current state of our planet).

Likewise, the theory of abiogenesis suggests that life was generated by different chemical reactions that gradually allowed the most primitive organisms to evolve .

7. Theory of underwater suction cups

Hydrothermal springs, also known as thermal water vents or hydrothermal underwater vents, are found deep in the ocean. These are cracks and fumaroles that allow the passage of steam and hot water. These vents have very extensive ecosystems. According to this theory, the nutrient-rich oceanic environment, along with reactive gases, may have created the habitat necessary to generate the first forms of life.

In other words, the origins of life as we know it could have taken place inside the hydrothermal vents ; a question that also takes up the proposals about what could have happened under the ice sheets that previously covered the oceans.

8. RNA (and protein) theory

Ribonucleic acid is the compound currently considered crucial in the organization and expression of our genetic material. It works together with deoxyribonucleic acid, DNA, transferring and systematizing the vital information that the latter generates. It is a kind of messenger of DNA and has the ability to regulate itself more automatically. The theory of the generation of life explained by RNA says that it occurred because of a spontaneous outbreak of RNA on our planet .

In the face of this, an important question has emerged: which came first: RNA or protein? Some theories postulate that without the synthesis of the latter, RNA could not have emerged, much less spontaneously; since the most basic components of proteins are too complex.

9. Theory of Genesis under the Mud

There is also the proposal that life on earth evolved from the concentration of mud. This is because such a concentration could serve as an area of condensation of chemical activity; which could eventually give rise to a kind of “breeding ground” for the components needed to generate genetic material (DNA and RNA).

10. Theory of metabolism

In contrast to RNA theories, theories of metabolism say very broadly that chemical elements and atmospheric nutrients simply continued to react over time, producing increasingly complex molecules . This gradually gave rise to the first forms of life and later to life as we know it.

Bibliographic references:

  • Marshall, M. (2016). The secret of how life on earth began. BBC. Retrieved July 10, 2018. Available at http://www.bbc.com/earth/story/20161026-the-secret-of-how-life-on-earth-began.
  • Futurism (2015). Abiogenesis: 7 scientific theories for the origin of life… and one new one! Retrieved July 10, 2018. Available at https://futurism.com/abiogenesis-7-scientific-theories-origin-life-one-new-one/.
  • Daminelli, A. & Santa Cruz, D. (2007). Origins of life. Estudos Avançados 21(59): 263-285.