Where does life come from?
That is still a mystery. Until the 19th century, scientists believed in spontaneous generation. “If you put a dirty shirt, seeds and a piece of cheese in a hermetically sealed recipient, then after some time, you will find a mouse” the Belgian doctor Jan Batist Van Helmont wrote completely seriously in 1650. It was the experiments of Louis Pasteur that put an end to this belief.
The theory of “vital force”, which stated as a principle that only living matter could manufacture the elements of which it consists, was overtaken in 1953 when Stanley Miller, a young student preparing his thesis, carried out an experiment that made him famous. He prepared a mixture of hydrogen, steam, methane and ammonia, meant to represent the composition of Earth’s original atmosphere and containing the four main elements making up living (organic) matter: carbon, hydrogen, oxygen and nitrogen. Then he subjected this mixture to electrical discharges simulating lightning and solar radiation. After letting it rest for several days, he was surprised to find cyanhydric acid, carboxylic acids and several amino acids … in short, a part of the elementary “building bricks” of life. However even if we know how to simulate the fabrication of the “bricks”, no-one has yet been capable of artificially constructing the “building”, a living cell with its reproductive material based on DNA. And nothing indicates that one day we will manage to do so. Created in the oceanic trenches near hot hydrothermal springs? By catalysis on the surface of certain damp rocks under bombardment by solar radiation much stronger than it is today? By panspermia, that is to say from very primitive living organisms travelling through space on comets or asteroids arriving from outside the solar system? Or by “something else”? At present, no one knows.
All living beings on Earth, including human beings, are the descendants of these very old original living cells. Between the creation of primitive cells and the animals, plants and human beings of today, time has elapsed, a lot of time. Time necessary for the appearance and evolution of more and more complex and more and more specialised organisms adapted to their environment and living beside some of the survivors of species that had appeared earlier. Life making billions of trials and errors before a new viable being was generated, more evolved than its ancestors. Hundreds of thousands of years before certain monkeys that have disappeared today began to stand up and walk erect whilst at the same time the fingers of their feet atrophied to become toes. And, life had a hard life! Destructive climatic changes, waves of volcanic eruptions, cataclysmic collision with a giant asteroid, colossal fires on a planetary scale, each time life fought back against catastrophe, even if many species were lost on the way! |