Why did it rain for millions of years in prehistory

There was no heavy rain for millions of years in prehistory. This was fabricated by some completely unprofessional self-media to scare people’s attention. Generally speaking, "heavy rains of millions of years" refer to the Carnian flood event in the middle and late Triassic period. This was actually a major turning point in the global climate from drought to humidity, but it did not mean "rainfall". "Millions of years of rain", but the global climate was relatively humid for millions of years, with frequent rainy seasons and floods. To understand this, we have to start with the climate of the Triassic. The Triassic Period began 252 million years ago. It inherited the distribution pattern of land and sea from the Permian Period. Almost all the land on the earth was put together to form Pangea. From the Early Triassic to the Middle Triassic, Pangea became closer and closer, reaching its peak in the Middle Triassic about 240 million years ago.

In addition, the Triassic also inherited the high temperature and arid climate of the Permian. The large-scale magma overflow at the end of the Permian caused the earth's temperature to rise rapidly. The carbon dioxide content originally caused by large-scale forest growth in the Carboniferous and early Permian periods decreased and the cold environment changed. Under the influence of the huge amounts of carbon dioxide emitted by magma overflows, the earth's temperature at the end of the Permian and early Triassic may have risen by about 8°C, and the polar ice caps completely disappeared.

At the same time, the huge Pangea stretched from Antarctica to the North Pole when it was at its largest, and because of its huge area and relatively high average altitude, it not only cut off ocean currents, but also formed a huge heat source on the land (the specific heat capacity of rocks is relatively small, and after sunlight It heats up faster than sea water, and because of its high altitude, it receives more heat from the sun), resulting in a huge temperature difference between sea and land, and the strongest monsoon climate in the history of the earth. Under the monsoon climate, a huge desert area is formed in the inland areas of Pangea's equator and mid-latitudes. It only gets rainfall in a few months in summer, and it is almost completely dry in other times. The deeper you go inland, the more... in this way. Under the influence of these two factors, the early to middle Triassic was basically arid and hot conditions.

However, this climate suddenly changed in the Late Triassic. Starting from the middle of the Carnian period (234-232 million years ago), the earth's climate suddenly became humid and rainy. This humid and rainy stage lasted for nearly 2 million years. time. Scientists found that the lithology of the strata during this period suddenly changed from carbonate rock (limestone and dolomite) to black shale or siliceous rock. Carbonate rocks are generally formed in hot shallow seas, due to seawater The rapid evaporation of seawater makes the calcium and magnesium ions in seawater supersaturated, so they react with carbon dioxide to form limestone and dolomite; shale is formed due to the deepening of water depth and the precipitation of tiny muddy sediments from land in deep water. The same is true for siliceous rocks. This is due to the enhanced weathering of land, the rapid disappearance of easily weathered materials in rocks, and the remaining siliceous components that are difficult to weather and are brought to the ocean for precipitation. In addition, scientists also found a series of evidences such as an increase in organic soil and moist soil in the terrestrial environment at that time, and an increase in the content of hygrophilic plant pollen.

This climate change that occurred during the Carnian period is called the "Carnian humid episode" or the "Carnian flood event." Many self-media often refer to it as "the Triassic period, when the Earth fell "Millions of years of rain" is, of course, a very exaggerated and incorrect statement. The fact is that this period was only humid and rainy, and the earth changed from a hot and arid climate to a hot and humid climate.

Why did the Carnian flood event occur?

There are currently two mainstream views: Some scholars believe that the continuous aggregation and uplift of Pangea to form higher terrain has had a strong impact on the global atmospheric circulation system, leading to the formation of a super monsoon climate, which is reflected in the northern hemisphere as the winter prevailing southward across the ancient Teti The dry northerly winds of the Sri Lankan Ocean and the moist southerly winds that prevailed northward in summer and brought heavy rainfall to the northern shore of the Paleo-Tethys Ocean contributed to the increase in humidity in the Paleo-Tethys domain. Recently, new evidence shows that the eruption of the Wlangoria Large Igneous Province may be the main cause of the event: the volcanic eruption caused CO2 and other greenhouse gases (such as SO2) to be emitted into the atmosphere, causing ocean acidification and global warming, causing weathering and increased denudation rates, resulting in the demise of carbonate platforms and the deposition of massive siliciclastics. However, although this event has been studied for nearly 30 years, its specific triggering mechanism is still unclear, and more geological evidence and richer research methods are needed to solve it.