A look at the past
Some geological evidence proves that there have been climatic ‘crises’ on a large scale that have modified the distribution of creatures living on Earth. Recent geological and paleontological researches seem to indicate that in at least one of these crises the role played by methane hydrates could have been very important. 55 million years ago, between the Paleocene and the Eocene, on our planet a climatic and environmental catastrophe of enormous proportions took place, known to researchers as the Paleocene-Eocene Thermal Maximum (PETM). The global warming, that involved the whole planet, brought about migrations of animals on the mainland from subtropical zones to higher latitudes, while 70% of the creatures living on the ocean floor died out. As a consequence of conditions that have not yet been understood (but probably a result of a period of intense volcanic activity) the oceans got warmer provoking the release of enormous quantities of methane from the ocean floor that then entered the atmosphere. The amount of gas is in the order of billions of tonnes released in the time interval of a couple of millenniums, or perhaps, even a few centuries. The melting of the hydrates made the continental slopes unstable and these, sliding and falling, released more methane creating a cyclic process that was self-powered for a period that lasted between 80,000 and 200,000 years.
The greenhouse effect that the released methane triggered off, heated the oceans more and more, bringing about the release of other methane and a reduction of the oxygen dissolved in sea water causing serious damage to sea life. In the Nineties, the analysis of marine sediments and of their paleontological content has led to estimate the rise in temperature of the oceans as having been around 8-10°C. This resulted in a modification of both oceanic and atmospheric circulation bringing about intense climate modifications and the extinction of numerous forms of life.
Other ‘crises’ of this kind are documented in the geological history of the Earth, for example, 250 million years ago, in the Permian or at the beginning of the Jurassic. For these events that are so far back in time, there are no geological proofs to indicate a relationship with methane hydrates. In a more recent past, instead, the analysis of ocean sediments and the study of the presence of bacteria that feed on methane show that in different parts of the world, the warmest spells of the last glacial period always correspond to the presence of great quantities of methane, released from beneath the sea floor (70,000 to 12,000 years ago). Some scientists who are studying the problem of global warming, fear that an increase in temperature on our planet can in turn trigger off a sudden release of the methane contained in the hydrates.
Now that methane hydrates have been discovered, they are proving to be present on sea floors in enormous quantities. As already mentioned, some researchers suppose that it is the very methane hydrates that act as the ‘adhesive’ that allows the stability of the sediments that are deposited along the continental slopes. Therefore the rapid melting of methane hydrates would have the immediate effect of destabilising the sediments that have accumulated along these slopes. This could set off underwater landslide phenomena, even on a vast scale, that could in turn bring about the propagation of anomalous waves.
Unconventional gas: shale gas
Con la graduale scomparsa del ghiaccio marino in seguito al...
The melting of the ice cells, not only brings about the release of methane gas, but it also produces another important substance: fresh water