One of the specificities of the TerreTerre is to have a mechanism of resilienceresilience climate which allows it to stabilize the surface temperature, in particular by regulating the level of CO2 in L’atmosphereatmosphere. This mechanism, which is an integral part of the carbon cycle, is based on a series of physico-chemical reactions which involves the alteration of mineralsminerals silicates. As described in a previous article (see below), this mechanism has been particularly effective for several billion years, allowing, despite the multiple climatic crises experienced by the planet, to fall each time into conditions of acceptable habitability for living organisms.
A more or less effective mechanism depending on the temperature
The chemical alteration of silicate minerals, which essentially make up the earth’s crust, is indeed a major consumer of CO2. In return, the carbonecarbone is trapped in the form of bicarbonatebicarbonate, which after being transported by rivers, will end up at the bottom of the oceans where it will be stored for several million years. As effective as it is, this resilience mechanism is not measurable on a human scale. Its effects are only observable over several tens or even hundreds of thousands of years. It will therefore not be necessary to count on it in the short term to absorb the massive excess of CO2 that Humanity is emitting into the atmosphere. In the history of the Earth, however, this is an almost trivial delay and understanding the workings of this mechanism is essential to better understand the past and future climatic evolution of our Planet.
A new study has therefore looked in detail at the factors influencing the weathering of silicates. Previous studies have shown that this is a strongly temperature-dependent mechanism: the higher the surface temperature, the more efficient the weathering and pumps CO2, lowering its rate in the atmosphere and thus cooling the atmosphere. Conversely, the lower the surface temperature, the less the mechanism works. CO levels2 then rise, allowing the heating of the weatherweather. A great balance. But all is not so simple. Because it’s not just the temperature that comes into play.
Sufficient water and minerals
The study, published in Science, indeed shows that the quantity of minerals made available by erosion must also be sufficient, as well as water. Water is an important point, since it is essential to the weathering reaction. Remove either and the mechanism will be less efficient, even under conditions of rising temperatures. The vitessevitesse supply of silicate minerals is also a limiting factor. The authors note that when rock erosion rates are low, the mechanism becomes insensitive to temperature. Conversely, the strong continental erosion that the Earth would have known in the last 10 to 15 million years would have allowed this mechanism to thermostatthermostat to be more sensitive and efficient. Namely: erosion rates are intimately linked to the formation of high reliefs and therefore to plate tectonics.
Quantifying the process exactly remains difficult, however. Because other reactions indeed accompany the alteration of silicates. This is theoxidationoxidation from mattermatter organic matter trapped in rocks and sulphidessulphides. However, these reactions themselves emit CO2.
Although the details of its operation are not yet known, this terrestrial thermostat appears to be so effective that some researchers are proposing to spread crushed silicates in cultivated areas to increase CO capture.2 and reach the carbon neutralitycarbon neutrality. However, the feasibility of such a project remains uncertain, especially when you consider that a lot of water must also be brought in. A problematic point in the context of droughtsdroughts repeated that we currently know.
Like the current climate crisis, the Earth has experienced many temperature variations in its history, sometimes extreme and resulting in mass extinctionsmass extinctions. Yet the climate has always managed to regulate itself following these dramatic events, suggesting the existence of a powerful resilience mechanism. According to this new study, this mechanism, linked to the alteration of silicates, would be of the order of 100,000 years.
Article of Morgane GillardMorgane Gillard published on November 18, 2022
If we are currently on the verge of a climatic catastrophe, it is however not the first time that the Earth has experienced this kind of crisis. The history of our Planet is indeed punctuated by many climatic variations, sometimes extreme, whether glaciationsglaciations or periods of intense warming. Some of these episodes are also associated with mass extinctions. These events have played a major role in the history of life on Earth, because if they are associated with a collapsecollapse of biodiversity, they have enabled theemergenceemergence news speciesspecies. A process which, one thing led to another, led to the appearance ofA wise man.
Extreme climatic crises in the end still resolved
It therefore appears clearly that despite these dramatic episodes to which the earth’s environment has been subjected, life, during its 3.7 billion years of existence, has always succeeded in resuming its development. And this thanks to a mechanism of climate resilience which has, each time, enabled the Earth’s climate to return to stable global temperatures favorable to the development of species. Even after catastrophic events such as the Paleocene-Eocene thermal maximumPaleocene-Eocene thermal maximum about 55 million years ago, during which the temperature increased by +5 to +9°C to reach a global average value of 32°C during the peak, the Earth was not permanently transformed into a hell arid and unlivable. Gradually, physico-chemical mechanisms have made it possible to lower temperatures and fall back to a more acceptable average for living species. For MIT scientists (Massachusetts Institute of Technology), it is moreover necessary that such a mechanism of resilience exists, because otherwise the global temperatures would have only gradually increased. However, this is clearly not what is observed ingeologic time scalegeologic time scale.
For the researchers, this resilience is closely linked to the weathering mechanism of silicates, a geological process that takes place on a microscopic scale and which involves chemical reactionschemical reactions which regulate the level of CO2 in the air.
A resilience mechanism that plays out continuously under our feet
Because the problem of CO2 is not new. Each episode of extreme global warming has been associated with very high levels of this greenhouse gas in the atmosphere. However, it turns out that the CO2 is one of moleculesmolecules who enters thechemical equationchemical equation weathering of certain silicate minerals by water.
As a reminder, the continental crust is mainly composed of silicate minerals, such as feldspars and quartzquartzwhich enter into the composition of igneous rocksigneous rocks. The surface of the Earth’s crustEarth’s crust is however subject to the action of water (bad weather, rivers, etc.), which will gradually, by chemical reaction, alter these minerals to produce new ones. Thus, in the presence of water and CO2anorthite (plagioclase feldspar) decomposes to form ions calciumcalcium (Ca2+), of the ionsions bicarbonates (HCO3–), is a new mineral, kaolinite, which is a simple form ofclayclay. This reaction therefore consumes water and a lot of CO2. The products of this reaction will be transported by rivers to the oceans. There, the clays will sediment, while the calcium and bicarbonate ions will be used by marine organisms to produce their shellshell. Even though this precipitation reaction will then produce CO2, it is in less quantity compared to the consumption generated during the alteration. Once the organisms are dead, their shells, composed of CaCO3, will settle on the ocean floor to be stored there for millions of years. In the end, it appears that the CO balance2 of this cycle is negative, so that silicate weathering and the general carbonate-silicate cycle are considered carbon sinks.
A return to normal after a few hundred thousand years
As a result, the role of this cycle in climate regulation has long been scrutinized by scientists. In a new study published in the journal Science Advances, researchers at MIT have just demonstrated that this mechanism is indeed responsible for rebalancing the climate after climatic crises, at least those that have occurred over the last 66 million years. Their results, based on numerical simulationsnumerical simulations, show that if this mechanism seems very efficient, it is also very long. Climate resilience would thus take around 100,000 years or more. A durationduration short on the geological time scale, but rather long on the human scale! While this news is therefore positive, in a certain sense, since it implies that the current global warming will one day be slowed down and that the climate will gradually regain a balance, the duration of the resilience mechanism means that this does not change our immediate problems. nor to those that future generations will know.
Earth will recover, yes, life too, one way or another. But our societies? This is much less certain, unless we decide to act to limit warming before the process gets carried away. And it is high time.
