Let me tell you a story based on facts published some years ago. Specifically, new findings on the biology of plesiosaursin calculations on fees of species extinction and in some advances on ecological aspects of global phenomena such as the one that occurred a few years ago. 200 million yearsThis is the point at which we place our protagonist.
Kansas swam, enjoying the sun and the coolness of the water. Occasionally, she would dive after a school of fish and return to the surface to warm up and keep an eye on the young. She was a really big plesiosaur, weighing several tons and the oldest of the herd. She enjoyed a relatively quiet life, typical of one who is known to be at the top of the trophic network . Just as her parents had done with her, Kansas had taught her offspring where to find the best prey, to protect themselves from storms and to be wary of some of their neighbours. The world, seemingly unchanging, went by without any major upheavals or major novelties. However, he had the feeling that the sea no longer tasted like it used to and that nowadays the prey seemed smaller and scarcer. The teenagers looked at him with disdain when he talked about such things. And maybe they were right. Maybe it was her perspective on the world that had changed. After all, she, too, remembered how exaggerated her grandmother seemed to her.
Our protagonists could hardly have known the dramatic processes that had begun thousands of years before, altering the Chemistry of oceans and atmosphere while radically modifying the shape of the emerged lands. Pangaea, the great supercontinent, was beginning to break up, ushering in the Jurassic era in which dinosaurs would dominate the Earth. Once again, the Earth's crust set to work to reshape the face of our planet. Billions of tonnes of sulphur oxides, carbon and other gases were added to the atmosphere, radically influencing the global climate. Temperatures rose, causing methane deposits to melt, which in turn fuelled global warming. New seas opened up and vast territories went under water while others emerged to receive the light of a sun they remembered as much younger. Too many changes to go unnoticed by the biosphere. The fossil record tells us that about 80% of species disappeared in this time period. Kansas could not have known this, but it was experiencing the Triassic-Jurassic (TJ) extinction first hand.
This subject of catastrophic events are known as mass extinctions. There is nothing biologically exceptional about species going extinct - it happens all the time. However, during mass extinction events the issue of disappearances is extraordinarily large (typically considered to be losses of more than 75% of known diversity) and rapid. To date, five major events have been identified in which the magnitude and speed of extinction abruptly break the scale: three before the TJ (in the Ordovician, Devonian and Permian) and one 135 million years later, in the Cretaceous-Tertiary transition (KT), which wiped out internship all dinosaurs.
But catastrophic, abrupt and rapid are adjectives that conjure up an image that is out of touch with reality. We are talking about planetary-scale phenomena involving unimaginable amounts of energy. The dimensions of time and space are so large that even geological moments labelled as dramatic changes can span hundreds of thousands or millions of years. It is very difficult to determine how long a mass extinction event lasts, but estimates always speak of several million years (except perhaps in the case of the KT, where the meteorite collision may have caused an impact on decadal or smaller scales). In addition, recorded extinctions in the oceans and on land may be millions of years out of date due to complex chain effects within the network of biosphere interactions.
Since humankind has begun to exert a significant effect on ecosystems (say 10,000 years ago), many species have disappeared directly or indirectly because of us. The figures for the best-known groups (such as mammals, birds and amphibians) suggest that we are far from 75%, but in some groups the percentages of species threatened with extinction (species that are likely to disappear in the near future) are close to 50%. As for speed, there is no doubt. The current rate of extinction would lead us, in an equivalent geological time, to an impact on biodiversity comparable to that of the previous five major extinctions. We are, like Kansas, witnessing a major mass extinction event.
The TJ extinction lasted several million years and did not noticeably affect plesiosaurs but did affect the diversity of several groups of gastropod molluscs, cephalopods and bivalves, marine sponges and some dominant groups of terrestrial tetrapods such as the thectopods. Having enjoyed the wonders of the ocean all her life, Kansas could never have imagined being in the midst of one of the greatest extinction events in Earth's history. Like her, we may be living with the effects of a great extinction in progress, but not realise it because we are short-sighted. In science, being short-sighted is tantamount to not having enough information. We need to know more, to have larger time series from data to address ecological questions core topic to understand what is happening to Biodiversity. The impact we have had on the biosphere is on the way to being equivalent to that of the events that triggered the great extinctions of our planet. This time we are not dealing with an asteroid impact, a global geological phenomenon or uncontrollable astronomical circumstances. The current biodiversity crisis lies in the way we interact with nature. The sooner we address the topic of resource exploitation, resource sharing and waste management , the sooner we will slow down the current rate of extinction.
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David Galicia
researcher of Biodiversity and Environment Institute andprofessor of the School of Sciences of the University of Navarra.
