Supervolcanoes caused a mass extinction 200 million years ago.
According to the China Seismological Network Express, 200 million years ago, a mass extinction made more than half of the life on the earth disappear. Combined with previous geological research, the researchers roughly restored the extinction scene 200 million years ago: at that time, a "super volcano" on land continued to erupt for nearly 600 thousand years, forming a large-scale magma deposition across North America and Pangea. Volcanoes released a lot of carbon dioxide and methane gas into the atmosphere, making the concentration of carbon dioxide about 10 times that of the present. Increasing greenhouse gases lead to climate warming, lack of oxygen in the ocean and acidification of seawater, and aggravate continental weathering. This process lasted about 2 million years. A large number of creatures can't adapt to drastic environmental changes and eventually disappear from the earth.
"However, this extinction also provides room for other creatures to develop. Soon after, dinosaurs appeared and began their journey of hegemony for more than 654.38 billion years. " Shen Jun, the first author of the paper and a researcher at China Geo University, said.
Why did dinosaurs become extinct?
Most scientists speculate that this extinction event was caused by one or more reasons, such as an impact event caused by an asteroid or comet, or a long volcanic eruption. The volcanic eruption of craters such as chicxulub crater and Deccan dark rocks is close to the Cretaceous-Paleogene boundary, which is considered to be the most likely cause of this extinction event. Impact events or volcanic eruptions send a lot of dust into the atmosphere, blocking sunlight and reducing photosynthesis of plants, thus affecting ecosystems around the world. However, a few scientists believe that this extinction event occurred slowly, and the reason for extinction was the gradually changing sea level and climate.
In 2004, J. David Archibald and David E. Fastovsky tried to put forward an extinction theory that combined many causes, including volcanic eruption, regression and impact events. Dinosaurs were the largest vertebrates at that time. They were first affected by environmental changes, and their diversity began to decline. Suspended particles ejected by volcanic eruptions gradually cool and dry the global climate. Finally, the impact event led to the collapse of the food chain dependent on photosynthesis, which impacted the already declining land food chain and marine food chain. The difference between multi-cause theory and single-cause theory is that it is difficult to realize large-scale extinction events and explain the mode of extinction by single cause.
Extinction mode
Although the Cretaceous-Paleogene extinction events led to the extinction of many species, different evolutionary branches or within each evolutionary branch showed obviously different extinction degrees. Because the particles in the atmosphere block the sunlight and reduce the solar energy reaching the surface, the organisms that depend on photosynthesis decline or become extinct. In the late Cretaceous, the bottom of the food chain was composed of organisms that depended on photosynthesis, such as phytoplankton and land plants, as it is now. There is evidence that the number of herbivores has decreased due to the decrease of plants on which they depend; Similarly, top predators (such as Tyrannosaurus rex) have also been affected.
Coccidian, mollusks (including ammonites, thick-shelled clams, aquatic snails and mussels), and animals that feed on the above-mentioned hard-shelled animals all perished in this extinction event, or suffered a serious blow. For example, black dragon is believed to feed on ammonites, a group of marine reptiles that became extinct in the Cretaceous-Paleogene extinction event.
Omnivores, insectivores and scavengers survived this extinction event, probably because their eating habits have changed greatly. There seems to be no completely herbivorous or carnivorous mammals at the end of Cretaceous. Mammals and birds survived the K-Pg incident by feeding on insects, earthworms, snails and other animals. These animals feed on dead plants and animals. Scientists assume that these creatures live on organic fragments of organisms, so they can survive this extinction event of flora collapse.
In the river biological community, only a few animals are extinct; Because the river biological community mainly depends on the biological organic debris washed down from the land, and less directly depends on the living plants. The ocean has a similar situation, but it is more complicated. Animals living in planktonic areas are far more affected than those living on the seabed. Animals living in the plankton zone almost feed on living phytoplankton, while animals living on the seabed feed on bio-organic debris, or can be transformed into bio-organic debris.
Among the creatures that survived this extinction event, the largest land animals are crocodiles and dinosaurs. They are semi-aquatic animals and can feed on biological remains. Modern crocodiles can eat carrion for a living and can not eat for months; Young crocodiles are small and grow slowly. In the first few years, they ate invertebrates and dead creatures. These characteristics may be the key to the survival of crocodiles in the extinction event at the end of Cretaceous.
After the extinction event, many vacant niches were created, and it took a long time for the ecosystem to recover its original diversity.