C'è forse un po' di allarmismo.
Ma sostanzialmente è vero che l'Uomo si sta comportando con la Terra come un agente infettivo troppo avido nei confronti del proprio ospite...
Un agente patogeno non troppo aggressivo (si pensi all'influenza) riesce infatti a vivere bene a spese della propria vittima, rispettandone le necessità di riproduzione e di sopravvivenza, in modo che ambedue possano coesistere a lungo nell'ambiente.
Un agente troppo aggressivo, invece, distrugge troppo efficacemente l'ospite e si estingue presto anch'egli (basta pensare ad Ebola).
Humans will have
wiped out 75%
of species by 2250
According to Australia Broadcasting Corporation (ABC News), Coffin told a conference in Hobart that humans will cause the sixth mass extinction event to face the planet. The last five mass extinctions, which have taken place over the last 550 million years, were caused by asteroids hitting Earth, climate fluctuations and volcanic eruptions. The most devastating event took place around 250 million years ago. In the Permian event, 96% of species were lost following the combination of a massive volcanic eruption in Siberia, global warming and deep sea anoxic waters. If 75% of Earth's species were wiped out, as Coffin predicts, the loss would be similar to the best known extinction event – the Cretaceous–Paleogene extinction event – when a massive asteroid wiped out about three quarters of all plant and animal life on Earth, including all the dinosaurs. "We're on a trajectory to reach the 75% level sometime between 240 and 2,000 years from now," he told ABC. "Based on all threatened species as defined by the International Union for the Conservation of Nature ... assuming all of those threatened species become extinct then we would reach mass extinction somewhere between 240 and 540 years from now." He estimates that there are around 8.7 million species on Earth today, excluding the creatures and plants yet to be discovered. "We've only [discovered] about 15 per cent. So there is still 85 per cent that are yet to be discovered and or described."
Discussing mankind's role in future mass extinction, he said "Homo sapiens have been around for 200,000 years - that's the length of our reign. The dinosaurs were around for 165 million years, so we're just a little blip on the geological time-scale. We haven't been around very long but we seem to be very good at driving a mass extinction ourselves." Animals that might survive the event include smaller ones that can breed quickly, such as cockroaches. "Species like us that don't reproduce until we're in our teens at earliest, with long gestation periods and that take a long time to evolve or adapt - big mammals - we're most vulnerable." However, Coffin also said he does not think mankind will kill all life on Earth: "Prior to the explosion of multi-cellular life 540 million years ago there were at least two episodes where the total surface of the Earth froze over - we call that a Snowball Earth. "There was single cell life back then, and even though the entire planet froze over some of that life survived. That's why we are here today."
Author: Hannah Osborne } Source: International Business Times [January 14, 2014]
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