José Manuel NievesSEGUIR Updated: Save Send news by mail electrónicoTu name *
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The history of life on the Earth it is long and complex. Began in some way as yet unknown causes at least 3.760 million years, which is the age of the bacteria fossil oldest known until now, and from that moment life started to grow and to diversify. But make no mistake, for the vast greater part of that very long time there were no animals, no plants, or anything that they would not be single-celled organisms. For more than 3,000 million years , in fact, the earthly life was limited to bacteria and other micro-organisms similar.
there Was you expect to make “only” a few 500 million years for the occurrence of the first creatures formed by more than a cell . Cells began to work together, sharing the tasks (transport, respiration, food processing, etc.) giving rise to the first animals themselves. Only from that point we can start to talk about “ life ” as we know it now. Sponges, fish, amphibians, reptiles, plants, dinosaurs, mammals… all of the creatures, in order, that the fossil record we’ve been giving away and that scientists have been identifying over the last century and a half.
During these last magical 500 million years ago, however, and as life was becoming more and more complex and varied, different episodes were about to be finished with her forever. Eruptions, massive meteorite impacts, deadly radiation from space… In total, we know five major mass extinctions , from the Ordovician-Silurian , about 439 million years ago, the most recent of all, the Cretaceous-Tertiary , the one that killed the dinosaurs, 65 million years ago. Between these two extremes we find the great extinction of the Devonian-Carboniferous , ago to 359 million years, the Permian Triassic , makes 251 million years, and the Triassic-Jurassic , makes 210 million years ago. In each of these occasions, between 75 and 95 percent of all species that lived at the time of the extinction are gone forever. It would seem that the nature itself was trying to put an end to his experiment of complex life to return to the box departure, to the endless time of life single-celled.
for decades, researchers have been striving to seek the “ guilty ” direct of each extinction. We know for certain, for example, that dinosaurs (along with the 76% of all living species) disappeared suddenly 65 million years ago (in just a few hundred thousands of years) after the fall of a large meteorite 10 km in diameter in what is now the Gulf of Mexico . And we also know that in the Triassic-Tertiary, the fragmentation of the old and huge supercontinent Pangea allowed for the depths of the Earth emerge in large columns of magma, causing the disappearance of nearly 80% of the species that inhabited the world some 210 million years ago.
And now an international team of scientists led by Brian Fields at the University of Illinois, just to provide evidence that suggests that the great extinction of the Devonian-Carboniferous, during which they succumbed for 82% of all species, due to the explosion of a star nearby in the form of a supernova. Their findings have just appeared in an article in the server prepublicaciones ArXiv.
The causes of the extinction
Ago to 359 million years ago, just in the limit between the periods of Devonian and Carboniferous the Earth has undergone, as we have said, the loss of the vast majority of the species that populated. The “butcher”, known as “ Crisis of Hangenberg ” it lasted for about 300,000 years, and scientists believe that was due to the depletion of the ozone layer, which would have allowed a great amount of ultraviolet radiation from the Sun to reach and damage life on our planet.
Now, What led to the disappearance of the ozone layer? A possible cause could have been the increase of water vapor in the lower stratosphere, which would have given rise to large amounts of elements capable of damaging the ozone. But the duration of this effect would have been too short to account for the prolonged crisis of the Hangenberg. Was missing, thus, finding another different mechanism.
In his article, Fields and his colleagues propose a new explanation: the culprit of the extinction of the Devonian-Carboniferous could be a supernova, a star explosion that released massive amounts of energy in the form of photons, ultraviolet light, X-rays and Gamma rays, among others. To be released by the explosion, the photons ultra energy collided with the particles of interstellar gas, acelerándolas and creating cosmic rays.
According to the researchers, cosmic ray generated by a supernova near you might have “ bathed ” continuously the Earth for over 100,000 years. And that would have caused the depletion of the ozone layer in a time scale, this time, consistent with the duration of the crisis Hangenberg. The impact of such an event would have been global, and its devastating effects on living species. Of course, there are other types of astronomical events able to damage the Earth’s biosphere, as the events of solar proton or gamma-ray bursts, but their short duration would that the planet would be affected for only a few years.
The researchers also suggest what type of supernova was able to be treated. As they explain, “the mass extinction was driven by a type of stellar explosion called” supernova core-collapse “, CNSC for its acronym in English. According to their calculations, a CNSC less than 10 parsec distance (about 33 light years) would be catastrophic for life on Earth, which would be within the so-called “radius of death” of this type of supernova. The team speculates that the star explosion that caused the crisis Hangenberg was some distance, about 20 parsecs, far enough away as to not exterminate completely the terrestrial biosphere, but close enough to cause the disappearance of a large number of species.
According to the study, the evidence that such a supernova actually existed could be found in the form of radioactive isotopes created by the explosion and deposited then in the Land. While some of these isotopes will have already disappeared, others, such as the samarium 146, uranium-235 or plutonium-244, have half-lives long enough to continue to exist today. In fact, even the discovery of just a few atoms of plutonium-244 in fossils from the Devonian period late corroborarían the hypothesis of the supernova. Now you have to do is look for these isotopes…
According to the researchers, in addition, also other extinctions prior to the Devonian-Carboniferous could have been caused by supernovae. The reason is that the stars tend to be born in groups, so if a star explosion hit Earth, others of the same group could also have done it previously. The events of the cosmos, therefore, seem to have been leading the history of life on our planet much more than scientists had suspected until now.
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