There are many parameters that influence the Earth’s climate. They can be external, such as variations in the Earth’s orbital parameters, the intensity of solar activity and the drops in meteoritesmeteoritesor linked to major geological processes that modify the carbon cycle such as major volcanic eruptions and the movementmovement tectonic plates. The latter greatly influences ocean currents, whose role on the climate is no longer in doubt. Finally, there is Man, who via the combustioncombustion of fossil fuels, leads to a rapid and unprecedented increase in CO levels2 in the air.
If we put this last cause aside, we realize that throughout its history, the TerreTerre has had many opportunities to undergo climatic changes throughout its history. Geological records thus bear witness to numerous fluctuations in temperatures, sometimes extreme.
Difficult climatic conditions to reconstruct for the primitive Earth
If our vision of the climatic past is rather clear for the most recent geological periods, the further back in time we go, the more blurred it becomes. The constant reworking of the continental surface by erosive and tectonic processes tends to erase geological markers, especially those allowing us to reconstruct the climate of the past, which are already not easy to find. Thus, if we assume that due to a atmosphereatmosphere richer in CO2 In the early days of the Earth, the climate must have been generally warmer than it is today, it is difficult to know the average temperature for example atarchaeaarchaeaespecially since the intensity of the SoleilSoleil was then less strong.
A rather warm climate in the Paleozoic and Mesozoic
Yes, the ProterozoicProterozoic (2.5 billion years to 542 million years) is marked rather by a series of glaciationsglaciationsthe era of PaleozoicPaleozoic is considered a rather warm period in Earth’s history. The atmosphere is indeed rich in greenhouse gasgreenhouse gas as the carbon dioxidecarbon dioxide and methane. CambrianCambrianit is estimated that average global temperatures were around 20 to 25°C (compared to 15°C currently). A situation that will worsen with the greenhouse effect at the beginning of theOrdovicianOrdovicianaround 485 million years ago, before a glaciation occurred between 460 and 440 million years ago. New warm and humid climatic periods will thus follow one another, notably in DevonianDevonian (416 to 359 million years) and CarboniferousCarboniferous (359 to 299 million years). The PermianPermian will end with an episode of heatheat and of droughtdrought extreme due to the eruption of StairsStairs from Siberia, which will release enormous quantities of CO2 in the atmosphere. This climate crisis, with average temperatures approaching 30°C, will cause a major mass extinction that will mark the transition with the TriasTrias and the entry into the era of MesozoicMesozoic.
This new era, which extends from 251 to 65 million years ago, will be generally warm, with no major glaciation having been recorded during this entire interval. Despite fluctuations and some colder periods, the climate of the Triassic, JurassicJurassic a you CretaceousCretaceous is thus warmer than at present, partly because of CO levels2 higher than today.
The Paleocene-Eocene Thermal Maximum: the warmest period in recent Earth history
The era of CenozoicCenozoicwhich begins after the extinction of the dinosaursdinosaursis the best characterized in terms of climate. It is marked by major climate upheavals, with extreme temperatures. The PaleocenePaleocene (66 to 56 million years) is thus marked by average temperatures of 30°C. The peak was reached 56 million years ago, during the Paleocene-Eocene thermal maximumPaleocene-Eocene thermal maximum (PETM). In the space of 20,000 years, temperatures rise by 5 to 8°C! This is certainly the hottest period in recent Earth history. In any case, it is the one that is best documented.
The PETM is often referred to as a hyperthermic event. Several causes have been suggested to explain this episode of extreme warming, but the most likely is the volcanismvolcanism. 12,000 gigatons of carbon were released into the atmosphere. The culprit could be the opening of the North Atlantic Ocean, proof that tectonic processes can be the cause of major climate disturbances. This opening between Europe and North America will be accompanied by theemissionemission important volumesvolumes of makemake at the level of the continental margins in formation. The injection of magmamagma in the sedimentssediments marine will also lead to a significant release of greenhouse gases, via the combustion of mattermatter organic. This very rapid disruption of the carbon cycle would thus have been at the origin of an unprecedented greenhouse effect.
