While Earth’s history often appears to us as a frenzied series of biological and climatic crises, there is a period during which almost nothing happened on a global scale. This episode of climatic, tectonic, biological and even dynamic stagnation when looking at the deep levels of the Earth, is commonly called the “boring billion”. A slightly pejorative term that some researchers are now calling to abandon in favor of the “balanced billion”.
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[EN VIDÉO] A billion years summarized in 40 seconds: plate tectonics Researchers have modeled the movements of tectonic plates over the last billion years.
We are used to considering the history of the Earth as a long continuous timeline, regularly punctuated by major events, some of them catastrophic. Geosciences teach us that over time, the earth’s surface has continued to evolve, mainly because of plate tectonics. While some continents opened to make way for new oceans, others collided, giving rise to high mountain ranges. Partly because of this perpetual evolution of the earth’s relief and the rearrangement of massesmasses continental, the climate has also evolved. GlaciationsGlaciations and periods of extreme warming followed one another, shaping the landscape. For their part, precipitation and volcanism have contributed to enriching the oceans with nutrients, thus promoting the development of living organisms. The evolution of terrestrial life, however, has not been a long, quiet river. Severe mass extinctions have interspersed periods of intense diversification.
The history of the Earth: a succession of crises of all kinds
In short, even if the film moved very slowly and each change can only be seen by considering periods of several million years, we cannot say that it was boring. And yet, there is an episode during which this formidable dynamic seems to have been put on hold. A bit as if the entire Earth had entered a phase of lethargy.
This episode begins in the middle of ProterozoicProterozoic, about 1.8 billion years ago. However, several major significant events in the history of the Earth occurred shortly before. The Huronian glaciation ended 300 million years earlier, the meltingmelting ice having led to significant leaching of continental surfaces and a massive contribution of nutrientsnutrients in the oceans, promoting the development of cyanobacteriacyanobacteria photosynthetics. The oxygen level then increased suddenly in theatmosphereatmosphere. This episode known as Great OxidationGreat Oxidation will lead to the appearance of organisms aerobicaerobic and the formation of ozone layerozone layerwhich, by absorbing a large part of the solar radiationsolar radiation ultravioletultravioletwill promote the diversification of living beings.
A phase of terrestrial lethargy that lasted a billion years
Then nothing. In the 1990s, the review of geological, biological and climatic events throughout Earth’s history revealed the existence of a period of stagnation, between 1.8 and 0.8 billion years. During these billion years that geologistsgeologists “boring billion” or “barren billion”, nothing particularly exciting is indeed going to happen. The climate will remain relatively constant, without episodes of major glaciation, which is unusual when looking at the rest of Earth’s climatic history. The land masses all come together in the equatorial zone to form the supercontinentsupercontinent Rodinia. No continental tear will be observed during this period which scientists consider to be a long tectonic stasis. On the other hand, the oceans appear relatively nutrient depleted. Oxygen levels, despite the Great Oxidation, are in fact still very low compared to current ones. Oxidation reactions, essential to supporting geochemical cycles, are then too weak. As a result, we observe an evolutionary stagnation of life.
And this situation will last for 1 billion years. That’s a long time, even for a geologist. The system will finally suddenly start up again 800 million years ago with the breakup of the supercontinent Rodinia. A new major phase of oxygenation will take place, a new glaciation, and life will resume its development in a frenetic way.
From boredom to balance
But does this period deserve to be disinterested and given such a pejorative term? In an article published in the magazine GSA Today, RossRoss Mitchell and David Evans invite us to reconsider this mysterious episode which represents a vast portion of earthly history. Would this apparent “stagnation” not in reality be the result of complex interactions between different major processes taking place on a global scale? Interactions which, for once, instead of degenerating into biological or climatic crises (which in reality only result from profound destabilization of natural cycles like that of the carboncarbon, for example) would on the contrary have led to an overall balance, to which we would certainly not be accustomed. Instead of talking about “boring billion”, shouldn’t we instead say “balanced billion”?
Understanding this episode in the history of the Earth would then amount to considering the formidable interconnections that exist between the deep dynamics of the planet (movementsmovements of the nucleus, convectionconvection mantle, volcanism), the surface (movement of plates, atmospheric and oceanic composition, climate, biological activity) and the other bodies of the Solar System, and to establish how, all together, they were able to bring about such a perfect planetary balance, on a such a long period. An incredible phenomenon of extremely delicate balance, when we know how easy it is to destabilize earth systems…