Mass extinction is the large scale loss of species on earth in relatively short periods due to environmental or climatic changes. Mass extinctions have been well documented in earths history thanks to the study of fossils and rocks by both paleontologists and geologists. Theories have been formulated to explain different mass extinctions on record. These include asteroid impact theory, climatic change theory, and the volcanic eruptions theory.
Asteroid impact theory
This occurred 65 million years ago a large asteroid hit the earth penetrating to the earth crust scattering dust and debris to the atmosphere. Fires were ignited due to the impact of , which incinerated millions of animals. Dust in the atmosphere blocked sunlight for years resulting in low temperatures that killed numerous warm-blooded animals that could not adapt to the low temperatures.
Global fires emitted high amounts of carbon dioxide, which and resulted in acid rain due to chemical changes in the atmosphere.Plants and phytoplankton that required sunlight for photosynthesis died out depleting food resources, thus affecting the food chain (Raup, 1992, p. 19). Herbivores that ate plants a starved to death, thus affecting carnivores animals this included the dinosaur.
This hypothesis was formulated by Dr. Robert T. Bakker in his book the dinosaur heresies. He speculated that large animals were able to cross large water bodies to reach far continents, thus bringing with them parasites and disease, and had developed some immunity to them. During close interactions, each animal succumbed to each others disease and small species were spared because of their inability to travel long distances.
Other scientists believe that small species were responsible for spreading parasites and diseases. Small species insects rapidly increased in population during the end of the Cretaceous period. Bugs that have been discovered contained malaria-causing parasites, and fossilized dinosaurs dung contained nematodes and protozoa (Warrick, 1998, p. 1).
Climate change theory
Volcanicity in Siberia or change in the course of the earth in orbit could have led to changes in climate, resulting in a rising in temperature globally 250 million years ago. This period known as the Permian saw 80 percent of life on land and 90 percent of the life of marine life perish. The same was also evident during the formation of continents with magma flowing over the earths surface.
This indubitably led to mass extinctions since a large number of animals were killed. High amounts of volcanic gases filled the atmosphere creating the greenhouse effect this led to increasing in temperature consequently resulted in melting of icecaps which led to flooding which wiped out large numbers of plants and animals on land. This theory is, perhaps the most suitable explanation for the mass extinctions of species.
This is because there is still evidence of climatic changes on earth and the effect of these changes is normally noticed by the migration of a score of animal species (Raup, 1992, p. 27). It can thus be speculated that the species that could not withstand the effects of global warming had to become extinct due to the adverse changes in climate.
Other theories explaining mass extinctions include the belief that the climatic effects of global warming continuously created harsh living conditions for some species leading to the death of many animals.
It is also believed that animals were at one point infected with serious contagious diseases that spread vastly and caused animals of certain species to be extinct. Still, on the , the release of greenhouse gases in the atmosphere continuously led to a reduction in the levels of oxygen in the atmosphere, which was challenging to some species leading to mass extinction.