<![CDATA[So far, scientists have identified five events in the history of our planet that led to the extinction of most species living on it. Now, an international team of researchers has suggested that there was another one, the Capitanian event, which occurred shortly before the already identified End Permian extinction, and reduced biodiversity by 96%. By “shortly”, the researchers mean around ten million years: the Capitanian event has been dated to 260 million years ago, while the End Permian event occurred 250 million years ago. The Capitanian event was discovered two decades ago, but little progress has been made on it since then because of the scarcity of evidence and the fact that it has only been found in the tropics. Now, a team led by palaeontologist David Bond from the University of Hull has ventured to the arctic instead, to the island of Spitsbergen, 890 km north of Norway, to examine its rocks. More specifically, the researchers are looking at the Kapp Starostin formation, which has been around since the Permian, and could give them some clues about the Capitanian event. Indeed, it has already yielded some clues from its layers. These layers contain the fossilised remains of sponges, organisms that lived in the Permian era, as well as brachiopods, a sort of mollusc whose shells are upper and lower, rather than left and right as are the shells of bivalves. The abundant brachiopod fossils abruptly disappear at one point in the Capitanian layers of the rock, Bond explains, suggesting a species reduction by as much as 87%, a scale similar to the extinction of the dinosaurs. The “abrupt” disappearance took about 10,000 years, no more than a blink on the geological scale. After that, some brachiopod species reappeared in the post-extinction layers of the rock, but the scene now belonged to bivalves, and this continued to be so until around 10 million years later when the End Permian event struck. Speaking about the reasons that led to the catastrophe, Bond said a likely candidate was the Emeishan Traps in China, a volcanic province which erupted during the period, filling the air with volcanic ash containing an abundance of carbon dioxide, sharply increasing the acidity of the oceans, and eventually wiping out most life on Earth. This eruption has been linked to the first evidence of the Capitanian event, which consisted of fossils found in China. The character and location of these first fossils are the basis for criticism of the new study, criticism that claims the Capitanian event was a regional occurrence, not a global catastrophe. However, Bond’s team did preliminary work to establish that the rock layers they were going to analyse corresponded temporally to the rocks examined in China. This involved an analysis of the ratios between carbon and strontium isotopes, reliable indicators of the age of a rock, as well as the presence or absence of different trace metals and magnetic polarities. Their analysis proved the correspondence, and after the examination of the fossils they concluded that the Capitanian event was not a regional occurrence in what is today Asia, but a global cataclysm that wiped out almost all life on Earth. The five mass extinction events so far recognised by science are, as follows, the Ordovician-Silurian event, which happened 443 million years ago, when life only existed in the ocean; the Late Devonian event from 359 million years ago, which wiped out 75% of all species on Earth; the late Permian event, the most destructive of all; the Triassic-Jurassic event from 200 million years ago, causing the extinction of half of the species on Earth at the time; and, the most recent one, the Cretaceous-Tertiary event that wiped out the dinosaurs. Image courtesy of Wikimedia Commons user: Jerzy Strzelecki]]>
Sixth Mass Extinction Suspected
