Let’s take things in order: we know that oxygen is important for marine life. This is even what started it all 540 million years ago, the beginning of the Cambrian era. At the time, life itself had already existed for three billion years, but that was where the more complex organisms arose, under water. It takes many millions of years again. And around minus 460 million: we observe a real explosion of marine biodiversity (these are not yet fish but, among the best known, there is the trilobite, which looks a bit like a small woodlouse.
How does oxygen get to the bottom of the ocean? that’s the whole question! it was thought until now that it came from the atmosphere. Well no ! And that’s the discovery of the day, published in the journal Nature thanks to the work of paleo-climatologists from the Biogeosciences laboratory in Dijon: it is plate tectonics that has changed everything. The configuration of the continents stirred the ocean, ventilated it. She brought the oxygen to the bottom. And underwater life was able to develop.
540 million years is an interesting period for researchers because we see life evolve in the ocean: this is explained by Alexandre Pohl, the main author of the study. This is the beginning of what is called the Phanerozoic (from the Greek phanero which means visible to the naked eye) When we look at the planispheres, there is only one large continent at the South Pole (the Australia is stuck to Africa with Antarctica, and South America) Some other pieces are “stroll” (Greenland and North America). For the rest, on a very large northern half, it is water with no oxygen. And yet, there is already oxygen in the air. This is therefore proof that it is not enough to oxygenate the ocean. What is interesting is that all this evolves from one map to another, in the study: sometimes the quantity of oxygen even regresses in the ocean: this is the case at the time of the five great extinctions mass that our planet has experienced.
We can go back so far in time and establish these maps by refining existing climate models, rather complex computer models and in 3D for the first time in this type of work. Thanks to sediments taken from the bottom of the water, we can analyze the fauna, make different measurements thanks to uranium, thorium, or even lead. All of this may shed some light, for example, in the future on the sixth mass extinction of biodiversity, which many scientists believe is underway.