In South Africa there is a mountainous region called Barberton. In it we can find one of the greatest riches in biodiversity on the planet, with more than 1,500 registered plant species, 350 birds and 80 species of other animals. But Barberton not only tells us about the enormous diversity of life that exists on the planet today; it also contains some of the oldest, best preserved, and least altered rocks on Earth . Barberton is one of the oldest regions on the planet; only the rocks of Isua, in Greenland, are earlier. And it is in them that scientists look for the oldest evidence of the existence of life on our planet, perhaps in the form of fossil bacteria. But where did they come from?
The origin of life has always intrigued us. However, it was not until 1922 when scientific research began. That year a 28-year-old Russian biochemist, Alexander I. Oparin , was presenting his ideas at a meeting of the Moscow Botanical Society. Nobody paid much attention to him until 1938, when the English version of his book appeared -published two years earlier- and where he fully presented his theories: at last there was a scientific hypothesis about how life could arise . The essential concept was that life arose from a hot, dilute soup of organic matter in the presence of a reducing, oxygen-free atmosphere. Lightning strikes, volcanoes and solar radiation collaborated by providing the energy necessary to form the complex molecules of life through the work and grace of the gradual and ineluctable mechanisms of chemical evolution.
But the real twist that made the origin of life a legitimate field of scientific inquiry happened in 1952. This time it fell to a young University of Chicago graduate named Stanley Miller, when he wanted to experimentally test his tutor’s ideas, Nobel laureate in chemistry Harold Urey, based on the Oparin. The original experiment lasted a week and was so simple that Scientific American published a way that anyone could reproduce it.
It all came down to a little boiling water, methane, ammonia, hydrogen, and sparks flying from electrodes . When he finished the flask was covered with an insoluble concoction, a very common by-product when organic reactions take place. But 15% hadn’t turned into that sticky tar. Miller asked Urey what he expected to find, and he replied: “The Belstein,” a multivolume manual describing millions of organic compounds. The wonderful thing about the experiment is that products belonging to the group of carboxylic acids appeared in considerable quantities. This tells us nothing, but if we remember that amino acids belong to this group , things change. Miller’s work caused a stir and many got down to work to take those results one step further. Nine years later the Spaniard Joan Oró, at the University of Houston, gave it by synthesizing one of the bases of DNA and RNA: adenine. The path to understand how the molecules of life appeared began to unravel.
Now, where did these molecules come from? Did they form on our planet or did they come from space? The latter idea, known as panspermia, was first enunciated by the Swedish chemist Svante Arrhenius in 1903, when he suggested that microscopic forms of life, such as spores, could be found in space and from time to time fall on a planet seeding it with lifetime. Is this possible? Maybe. In 1972 a meteorite, known as the Murchinson meteorite , fell in Australia, where 74 amino acids were found, of which 55 were of probable extraterrestrial origin.
If prebiotic chemistry is hidden behind an impenetrable veil, the mystery of where the first forms of life arose is no less a mystery. A first clue appeared in 1964, when biologist Thomas Brock, visiting Yellowstone National Park, discovered microbes in hot springs. The following summer he discovered algae that lived in places where the temperature reached 60ºC and bacteria in springs at 82ºC. To put it very bluntly, Brock found life in boiling water . Did life arise in this kind of environment, which can be found at subduction zones in ocean trenches, where crustal plates collide and sink under the adjoining plate? The truth is that the discovery of the so-called extremophilic microorganisms has expanded the restricted limits that biologists had imposed on life. Are they the common ancestor of all of us?
In the frozen region of Isua, in Greenland, the last piece of the puzzle is found. In rocks from 3.9 billion years ago , a strange ratio has been discovered between two isotopes , two types, of carbon: C-12 and C-13. They only differ in that one has one more neutron, which makes it slightly heavier. Despite the fact that both participate in the same way in chemical reactions, those of living organisms prefer the lighter one. And the Isua rocks have an abnormal amount of C-12 identical to that found in fossils and living beings .
Does this prove that life, along with oxygen, existed 3.9 billion years ago, only a few hundred million years after the formation of the Earth?
