Despite the fact that it seems that we are living in fin de siècle times, that the world is ending, that climate change towers over us like a sword of Damocles, our planet is far from being a harmonious world and at peace with itself. For that reason, if everything finally ends, it will be the sixth time that it happens .
Five mass extinctions have already taken place in the world (all of them before human beings existed) that wiped out practically all animal and plant life due to simple climatic hazards. The oldest of these extinctions occurred about 445 million years ago, and according to a new study published in Nature, it occurred because global climate cooling altered ocean current patterns and lowered marine oxygen levels .
Late Ordovician mass extinction
The Late Ordovician (LOME) mass extinction is the first or oldest of the five that have already taken place in our world. About 85% of marine species, most of which lived in shallow oceans near the continents.
Brachiopod fossils from the Ordovician period outcrop on Anticosti Island, Quebec, Canada.To find out exactly how this extinction occurred, measurements of the iodine concentration in carbonate rocks from that period were taken, contributing important findings on oxygen levels at various ocean depths. The concentration of the element iodine in carbonate rocks serves as an indicator of changes in the level of ocean oxygen in Earth’s history .
While the causes of the late Ordovician extinction have not been fully agreed, the study rules out changes in oxygenation as a sole explanation for this extinction and adds new data that favor temperature change as the death mechanism for LOME. As climate model expert Alexandre Pohl explains:
We were surprised to see an expanded anoxia at the bottom of the ocean, as anoxia in Earth’s history is generally associated with volcanism-induced global warming. In recent years, mounting evidence points to several episodes in Earth’s history when oxygen levels also dropped in cold climates.