The text below answers a question from 10-year-old Cora Weisner for the series “Children’s Questions, Science Answers”
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When we ask ourselves how living beings arose, we assume that an entity created them. But, despite the fact that most religions are strongly based on creation myths, with supernatural entities that created nature, the Universe and living beings, this is not what science has shown us. The Universe does not need a creator, natural laws well adjusted are enough to allow life to arise and evolve spontaneously, in places where some minimum conditions are satisfied.
The discussion about the origin of living beings on the planet is very old, and perhaps one of the first scientific reflections on the subject came with the Greek philosopher Thales of Miletus (639-544 BC). In trying to separate the mythological discussion from a more rational and general one, he made an important observation. Thales noticed that water was abundant on the planet, and that the existence of all living beings (at the time, animals and plants, as the microbial world was not known) seemed to depend on it. Thus, he postulated that life must have originated from water, and every organism deprived of it would die. Today we know that this is neither completely correct nor complete, but such a postulate has already brought about a very modern notion of life, centered on observations of the real world and not on philosophical or mythological speculations.
Science has addressed this difficult question from two main approaches: top-down (top-down) and from bottom to top (bottom-up). In both, the British naturalist Charles Darwin played a key role. One of the first scientists to systematically and comprehensively collect information on the diversity of life, living or fossil, he made a synthesis of life on the planet that would eventually result in his theory of evolution, one of the most classic applications of top-down study. , that is, starting from what is currently known and inferring the past. Today, based on modern genetic information, we know that there is a strong chance that we are all descended from the same ancestor, the Last Universal Common Ancestor or LUCA. Probably a microorganism that lived in the primitive seas and that would later diversify.
In the bottom-up approach, we build the complexity of life from simpler foundations: we start with isolated atoms and molecules and study the interaction between them and the context in which it would be possible to produce chemical entities complex enough to have characteristics of living beings, such as self-maintenance and self-reproduction. And here once again Darwin enters, as evidenced by the letter he wrote to his friend and botanist Joseph Hooker, in 1871, in which for the first time he formulated a model of the probable origin of biological entities from simpler chemical systems: “but What if (and how big if) we can imagine a hot little puddle with all sorts of ammonia and phosphoric salts – light, heat and electricity present – ​​and that a protein compound were chemically formed, ready to undergo even more complex changes […]”.
Darwin’s ideas for a purely chemical beginning of life impacted the scientific world, stimulating two researchers, one in England, John Haldane (1892-1964), and the other in Russia, Aleksandr Oparin (1894-1980), simultaneously and independently. , to create a theoretical model that would support this prebiotic chemistry, that is, the chemical reactions that precede life. Haldane and Oparin’s ideas could finally be put to the test in 1953, when researcher Harold Urey (1893-1981) and his then doctoral student Stanley Miller (1930-2007), at the University of Chicago, USA, recreated in the laboratory the conditions that the theoretical models had predicted. The surprising result was that, from very simple compounds and electrical discharges, it was possible to produce molecules that were previously considered to be uniquely biological, such as amino acids. Thus, prebiotic chemistry was consolidated as a research area, and many more experiments would be carried out from then on, to test the various stages of the origin of life.
Using both approaches, we are still learning how the original chemistry of the planet could spontaneously become more complex, giving rise to the first living beings capable of reproduction and transfer of information between generations. Once these entities emerged, it was only a matter of time (not short: hundreds of millions to billions of years…) for evolution to create the diversity of life we ​​know. There is nothing supernatural or mystical about the process, not even intention or directionality, but rather a complex dance between the different forces that govern nature, sometimes pulling towards chemical, molecular and biological diversity, sometimes towards extinction, elimination. , simplification.
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Douglas Galante is an astrobiologist and researcher at the National Center for Research in Energy and Materials.
