The exact origins of the first living cell from non-living matter is still a topic of scientific investigation and debate. However, there are several theories regarding how this might have occurred, and one of the most widely discussed is the theory of abiogenesis, also known as chemical evolution or the origin of life.
Abiogenesis proposes that under the right conditions on early Earth, organic molecules could have formed from simpler inorganic molecules through a series of chemical reactions. These organic molecules, such as amino acids and nucleotides, are the building blocks of life. Over time, these molecules could have further combined and interacted, eventually leading to the formation of a self-replicating system, which is one of the defining characteristics of life.
There are various experiments and observations that support the plausibility of abiogenesis. For example, in laboratory settings, scientists have been able to recreate some of the conditions thought to exist on early Earth and observed the formation of complex organic molecules. Additionally, meteorites and interstellar dust have been found to contain organic compounds, suggesting that similar processes might have occurred elsewhere in the universe.
As for how we would know if life originated elsewhere in the universe, scientists are actively searching for signs of extraterrestrial life through various methods. This includes studying environments in our own solar system, such as Mars and some of Jupiter's moons, where conditions might be suitable for life. Additionally, telescopes and missions are being used to search for habitable exoplanets (planets outside our solar system) and signs of life-indicating molecules in their atmospheres.
The discovery of even a single instance of extraterrestrial life, whether in the form of microbial organisms or more complex structures, would have profound implications for our understanding of life's origins and the prevalence of life in the universe. However, as of now, we do not have definitive evidence of extraterrestrial life, and the question of whether life exists beyond Earth remains a fascinating and ongoing area of scientific exploration.