Which Organisms Were Lost During the Cretaceous-Tertiary Extinction Event?

The Cretaceous-Tertiary extinction event is a large-scale species extinction event in the history of the earth. It occurred between the Mesozoic Cretaceous and Cenozoic Tertiary. About 65.5 million years ago, most of the animals and animals on the earth were extinct. Plants, including dinosaurs. The Cretaceous-Tertiary extinction event is famous for causing the extinction of dinosaurs and the rise of mammals. However, the Permian-Triassic extinction event wiped out about 90% of the life of the earth at that time, which was the worst in the geological age Mass extinction event.

Cretaceous-Tertiary extinction event

Although the Cretaceous-Tertiary extinction events caused the extinction of many species, different evolutionary branches, or within each evolutionary branch, showed significantly different degrees of extinction. As the particles in the atmosphere obscures the sun, reducing the amount of solar energy reaching the surface, biologically dependent photosynthetic decay or extinction. In the late Cretaceous, the bottom of the food chain was composed of photosynthetic-dependent organisms, such as phytoplankton and land plants, as they are today. Evidence suggests that herbivores have decreased in number as the plants they depend on have declined; similarly, top predators such as Tyrannosaurus have also been affected.

The duration of the Cretaceous-Tertiary extinction event has long been controversial because some theories believe that the process of this extinction event is very short (between years and thousands), while other theories It is believed that the process of extinction lasted a long time. Since it is impossible to find a complete fossil record of a species, the actual extinction time of an extinct species may be later than the final fossil record. Therefore, the elapsed time of the extinction event is difficult to measure. Scientists have found a small number of stratums with fossils across the KT boundary, dating from millions of years before the KT boundary to nearly one million years after the KT boundary.

Scientists have proposed several theories about the causes of the Cretaceous-Tertiary extinction events. Most of these theories focus on impact events or volcanic eruptions, and some theories even think that both are the cause. In 2004, J. David Archibald and David E. Fastovsky attempted to propose a theory of extinction that combines multiple causes, including volcanic eruptions, retreats, and impact events. In this theory, regressive events in the late Cretaceous period caused terrestrial and marine life communities to face habitat changes or disappearance. Dinosaurs were the largest vertebrates at that time. First, they were impacted by environmental changes, and diversity began to decline. The suspended particles emitted by the volcanic eruption have gradually cooled and dried the global climate. Finally, the impact event caused the food chain that relied on photosynthesis to collapse, and impacted the already declining terrestrial and marine food chains. The difference between the multi-cause theory and the single-cause theory is that it is difficult for a single cause to achieve a mass extinction event, and it is difficult to explain the pattern of extinction.