Origin of life

Representation of the early Earth.

Until now, the Big Bang theory is used to explain the appearance of the Earth. It is believed that our planet formed about 4.5 billion years, and for about a billion years, suffered important processes such as its cooling, enabling the emergence of life.

Scholars believed that the oldest living things arose spontaneously from raw material - the hypothesis of spontaneous generation, also called abiogenesis. However, through various experiments, performed by scientists as Redi, Needham, Spallanzani, and Pasteur was possible to rule out this hypothesis, adopting biogenesis, which states that the micro-organisms arise from preexisting others.

Even though I answered a big question, biogenesis does not explain how is the process of emergence of a species from another. Thus, there are a few explanations for this, being the origin of the chemical evolution more accepted by scientific category. This theory proposes that life arose from the arrangement between simple molecules, combined with environmental conditions peculiar molecules forming increasingly complex until the emergence of structures endowed with metabolism and capable of replicating itself, giving rise to the first living beings. Oparin and Haldane Miller are the forerunners of this hypothesis.

Currently, it is believed that the first living being was autotrophic. Two reasons justify its wide acceptance: the fact that the planet probably does not have organic molecules sufficient to sustain the multiplications of the first living beings until photosynthesis arose, and the fact that, due to the instability of the planet, these organisms could survive only if were in protected places such as hot springs underwater seas primitive. Thus, autotrophic hypothesis suggests that the first living things came first in the most extreme environments, feeding from the reaction between inorganic substances, such as some current archaeas: a process called chemosynthesis. This hypothesis suggests that, from these first organisms arose those capable of performing fermentation, then the photosynthetic and lastly, heterotrophic beings.

It is believed that these early people were prokaryotic, sharing many similarities with the archaea, and there are about two billion years ago, eukaryotic cell arose.

By Mariana Araguaia
Graduated in Biology
Team Brazil School