(Popular Science Times)
Recently, Chinese and British scientists published a paper in the American journal Science Advances, pointing out that after verifying all relevant geological and paleontological evidence, it was determined that the "Carney Flood Event" that occurred 233 million years ago was a biological mass extinction event.
Land landscapes of the Late Triassic
Friends living in the south will be impressed and unforgettable about the rainy season. In June and July, the warm and humid air flow of the Pacific Ocean brought by the southeast monsoon passes through the middle and lower reaches of the Yangtze River in China, resulting in persistent rainy days. This summer is no exception. However, this is not a big deal, and many friends may not know that in geological history, there has been a continuous rainstorm on The earth that lasted for millions of years. What exactly does it have to do?
This global environmental change occurred during the Carni period of the Late Triassic (237-227 million years ago). The "world map" of that time was very different from what it is today: all the land masses were connected together to form a "supercontinent" known as pancontinent. The surface of the Pancontinent is smooth, the climate is hot and dry, and almost dry. Early ancestor types of reptiles and mammals thrived in this sweltering land. By mid-to-late Early Kani (about 234-232 million years ago), the climate suddenly became humid, rainfall increased dramatically, black shale rich in plant stems and land-based clastic material imported from freshwater increased, and thick sediments from rivers, lakes, and coal swamps proved to be distributed around the world. The discovery of this phenomenon quickly set off a global research boom, and scientists referred to the extreme climate change events that occurred in the Late Triassic Kani period in geological history as the "Carnian Pluvial Episode" (CPE). Some scholars believe that it is the most significant biological and environmental-related event in the Mesozoic Era, and has had a huge impact on global ecosystems.
So, what changes have occurred on the earth due to such a long and long event?
Climate change is extremely volatile
The "Carni flood event" is a global event with rich geological records in deep-sea basins, shallow carbonate terraces and continental basins. Among them, the environmental changes in shallow carbonate terraces are more obvious, and from then on, the carbonate ecosystem dominated by microorganisms has changed to an ecosystem dominated by less productive offspring, and a real stony coral coral reef has emerged. At the same time, there have been hypoxia events in several regions.
A large amount of sedimentary evidence, such as the large number of evaporite rocks in the Southern Alps and the grain beach in the western Sichuan region, indicate that the monsoon hot and dry climate characteristics of the ancient Mediterranean coast in the late Triassic period continued in the early Carni period, and suddenly changed to a warm and humid climate during the CPE period, with increased rainfall and extremely turbulent climate change.
Biological evolution is wonderful and rich
During the CPE, the extinction rate at the marine life genus level was about 33 percent, ranking third among multiple extinction events in the Mesozoic Era. From the early to late Carney period, marine invertebrates decreased from 1129 genera to 775 genera.
Most marine biomes have similar trends, such as radiolarians, foraminifera, brachiopods, bivalves, etc. In particular, ammonite and tartarite, as important marine stratigraphic marker fossils of the Late Triassic, have found that ammonites reached a peak of extinction at the beginning of CPE, and the diversity of dendrite gradually decreased from 40 species in the early Carney period to 9 species. Even many groups of marine lilies of the echinoderm class became extinct during cpE. Who would have thought that before the CPE was proposed, some scholars joked that sea lilies don't like rainy days.
This heavy rain brings both destruction and redemption.
Some calcareous ultramicroplankton begin to occur, in which a rigid shell of calcium carbonate plays an important role in the carbon cycle between the atmosphere and the ocean. Bony fish suffered a major crisis during cpe, but sharks such as some cartilaginous fish began to radiate and evolve. The oldest turtles also appeared in the Karni formations of China.
The most remarkable aspect of terrestrial ecosystems during this period was the diversity and evolution of dinosaurs. Evidence suggests that dinosaurs appeared to have appeared about 243 million years ago, before the Carney period, but at that time they were scarce and dominated by carnivorous reptiles. By the end of the Carney period, both ornithischians and sauropods had emerged, and dinosaurs had become dominant species and ruled the planet for 160 million years.
The outcome caused by this heavy rainstorm had to make people doubt, and it turned out that "success is also Xiao He is also Xiao He".
In this baptism of rainstorms, plants are not far behind, a class of plants with particularly developed root systems and moisture tolerance began to rise, and quickly became the dominant taxon of global forests, which is gymnosperms such as conifers. Heavy rains turned arid grasslands, made up of low, drought-tolerant stone pines and arthropods, into forests of large conifers and large coal-forming plants. Before this heavy rain, the mainstream land animal beaked dragons, which could have lived happily, but now can only eat a limited number of plants, and the diodonts with few teeth and gastroliths have difficulty eating and digesting multi-fiber food, perhaps due to these factors, resulting in the gradual reduction of the number of binary beasts and beaked dragons in the Carney period, and the carnivorous main dragons also lost their food source and soon became extinct. Because dinosaurs have long necks, can also walk upright, have the advantage of feeding, and have developed teeth and stomach stones that help grind food, it can be said that "time, place and people" are occupied.
Due to the radiation evolution of conifers, amber appeared for the first time during this period, as well as early diverse insect taxa. Forests distributed around the globe brought rich and abundant tree canopy and prompted vertebrates to fly into the sky for the first time, and pterosaurs began their sky domination. The oldest crocodiles also appeared in the Late Kani period, and some phytoosaurs and lepidosaurs were widely distributed during the Kani period. The evolutionary history of mammals also began during the Carney period.
The reason for the CPE is a mystery
The discovery of fossils confirms the extinction of many species and radiation succession caused by the CPE period, when the Earth was still in the period of recovery and repair after the mass extinction at the end of the Permian, and the Carney period witnessed the rise of some taxa during this period, just as some organisms took a turn between ancient and modern times.
There has been no consensus on the causes of CPE. Scientists have proposed several hypotheses from the following aspects:
First, the tectonic movement of the plate causes the atmospheric circulation to change. Strong tectonic movements in the late Carboniferous period brought together the continents of Lauya and Gondwana to form the Pan-Continent. The aggregation of the pancontinent and the uplift of the central mountain range have had a strong impact on the global atmospheric circulation system, resulting in a super-monsoon climate. By the late Triassic period, the giant monsoon reached its peak, which further enhanced the land weathering, frequent seasonal rainfall, and the import of a large amount of fresh fresh water and land-based clastic debris, resulting in the demise of carbonate terraces, with a huge impact range.
The second is the convergence and collision of supercontinents, which triggers the eruption of igneous provinces (mantle column magma construction) to cause global climate disorders. Huge amounts of magma erupt from mantle column magma activity, releasing enough carbon dioxide to warm the globe. There have been at least three global temperature rises during cpE, varying around 4-6°C.
The third is caused by the interaction of comprehensive factors in the Earth system. In the early Triassic, global volcanic activity reached a climax, the seasonal circulation climate brought a large amount of rainfall and high concentrations of CO2 in the atmosphere combined, the ocean calcium planktonic microbial outbreak, the submarine plate activity and the outbreak of igneous provinces exacerbated the hypoxia environment in the ancient Mediterranean marginal sea area, a series of interplay factors contributed to this significant geological event.
The Carni flood event, which coincided in time with the large-scale evolutionary transformation of some organisms, heralded a new mass extinction event that played an important role in the reshuffling of land and marine life, and also marked the gradual formation of modern ecosystems, and dinosaurs undoubtedly became the biggest winners in this rainstorm.
(Author Liu Lu, Ph.D., Department of Scientific Research, Beijing Museum of Natural History)