Origin of Life: Theories, Oparin’s Hypothesis, and Cellular Evolution
Theories on the Origin of Life
What are the first theories explaining the origin of life on Earth?
Creationism is the basis of religion. In the West, the story of Genesis was long accepted literally.
Spontaneous generation, which Aristotle believed allowed some living things to be generated not only by their parents, was a prevailing thought around the third century. Francesco Redi delivered the first serious blow to proponents of this dogma. He experimentally proved that the white larvae of flies on meat are not spontaneously generated from putrefying meat. Later, Lazzaro Spallanzani showed that by heating and then sealing broth in containers, microorganisms were not generated while the vessels remained hermetically sealed. However, these findings were not fully accepted, as creationism and Aristotle’s influence remained strong in society.
Louis Pasteur irrefutably demonstrated in the nineteenth century that there was no spontaneous generation: living beings only arise from other living beings.
The theory of panspermia postulates that life arrived on Earth in the form of bacterial spores from outer space, driven by radiation pressure from stars.
Alexander Oparin’s Theory on the Origin of Life
Oparin proposed that chemical compounds present in the early atmosphere served as raw materials for the synthesis of simple organic compounds necessary for living beings. The first living systems appeared after a long period of prebiotic evolution in an aquatic environment, characterized by a lack of oxygen and frequent electrical discharges.
The Miller-Urey Experiment
Stanley Miller experimentally tested the early stages of Oparin’s theory. He created a circuit in which he:
- Introduced a glass container filled with boiling water.
- Added a mixture of gases that supposedly formed the primitive atmosphere (methane, ammonia, and hydrogen).
- Applied electrical discharges through electrodes, simulating the lightning that occurred in storms.
After cooling and analyzing the contents of the container, he found that several simple organic compounds, such as amino acids (the building blocks of life), had been synthesized.
Cellular Evolution: A Step-by-Step Process
- Appearance of the first cells (3800 million years ago): These cells were formed through a membrane that allowed the isolation of a set of molecules that reacted with each other, resulting in metabolism. This occurred in the aquatic environment, particularly in what is called the primordial soup.
- Emergence of prokaryotes (low organization): These were heterotrophic (obtaining organic matter from the environment) and fermentative.
- Selection of photosynthetic cells: These cells derived organic matter from inorganic matter, released oxygen (creating an oxidizing environment), were autotrophic (producing their own organic matter), and fermentative.
- Survival of heterotrophic aerobic organisms: These organisms used oxygen to oxidize organic matter and obtain energy.
- Appearance of basic eukaryotic cells (2700 million years ago).
- Evolution of complex eukaryotic cells: This occurred due to the endosymbiotic association of prokaryotes with basic eukaryotic cells, resulting in complex internal membrane structures.