ABSTRACT
Several mass extinctions have occurred during the Earth’s history. The Cretaceous – Tertiary Boundary (K-T) Extinction caused the loss of at least three-quarters of all species known at that time including the dinosaurs. The cause of this mass extinction is a controversial subject among scientists but the fossil evidence of it’s occurrence is abundant.
INTRODUCTION
The K-T Extinction occurred 65 million years ago. Many species perished in that extinction. Today evidence for this extinction can be seen in the fossil record. Biological, botanical and geological evidence at the Cretaceous – Tertiary Boundary show that some enormous event occurred that caused mass extinction of life on the Earth. Controversy about the cause of the K-T extinction exists with two main theories currently being in favour. One theory is called Intrinsic Gradualism and believes the cause of the K-T Extinction was a slow and gradual Earth generated event, caused by intense volcanic activity and the effect of plate tectonics. The second theory is known as Extrinsic Catastrophism and proposes that the K-T Extinction was caused by a sudden and violent catastrophic event such as the Earth being struck by a meteor or asteroid. The K-T Extinction supports the concept of Punctuated Equilibrium in evolution because surviving species evolved and others were exterminated. This creates the stepladder effect of evolution seen in the fossil record .
THE K-T EXTINCTION
The Cretaceous period occurred between 144 and 65 million years ago. The K-T Extinction is an event that happened at the end of this period 65 million years ago. By the beginning of the Tertiary period eighty-five percent of all species disappeared, making it the second largest mass extinction event in geological history (“The End-Cretaceous (K-T) Extinction”, accessed 2000).
Among the species that perished were the dinosaurs, pterosaurs, belemnoids, many species of plants, except ferns and seed-producing plants, ammonoids, marine reptiles and rudist bivalves. Severely affected organisms included planktic foraminifera, calcareous nannnoplankton, diatoms, dinoflagellates, brachiopods, mollusca, echinoids and fish. Mammals, birds, turtles, crocodiles, lizards, snakes and amphibians fared much better and were mostly unaffected by the End-Cretaceous mass extinction (“The End-cretaceous (K-T) Extinction”, accessed 2000...
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The possibility if a meteor strike as the cause of extinctions is discarded, something that most specialists agree on. There is no evidence of any meteor crater big enough or recent enough to be accountable for it; there are no “elements that are common extraterrestrially but less so on Earth, such as iridium, and no sign of a tsunami or other phenomena following the impact.” The extinctions where also very selective and occurred over a very long period of time. If a “one shot” catastrophe had been the cause it would have affected all species at the same time and in similar
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Throughout Earth’s history there have been many changes. These changes have consisted of temperature fluctuations, atmospheric differentiations, extinctions of various plant and animal life, etc. Over time everything seems to have evolved in some way form or fashion. However, the Permian Era extinction was different from all the rest. This extinction affected every form of life, but especially the marine life. Researchers have stated that 93-97% of all Earths species went extinct during this period of time. This essay will explain how a once blossoming progressive era turned into Earths most catastrophic event.
The most significant event of the Cretaceous era came at its end. Nearly 65 million years ago, the second most severe mass extinction in earth’s history occurred. This resulted in the loss of around 80% of species living at the time. Though nowhere near as severe as the end-Permian mass extinction, the end-Cretaceous extinction is the most well known mass extinction event. This is due to the violent event that caused it the extinction, as well as the chapter of earth’s history that it closed: the Dinosaurs. The Cretaceous Event ( often shortened to K-T event) Of the animals that were killed off were the flying reptiles (pterosaurs) and the last few mosasaurs and plesiosaurs, both early marine reptiles. Many mollusks and species of microscopic plankton were killed. Terrestrial plants suffered mass extinction as well. Almost 60% of terrestrial plants were lost. This led to high extinction rates among insect populations, especially insects that were highly specialized to feed on just a few types of plants had it the worst. It took approximately 9 million years for the global insect populations to recover from the Cretaceous extinction. Immediately after the extinction, the earth saw an explosion of short term species who respond well to fire, or other external disturbance. Evidence of the catastrophe comes from a thin rock layer deposited worldwide just after the impact. It is dominated by fossil plants whose descendants recover quickly after fires of other disturbances, such as Fire Weed in Alaska. The causes of the Cretaceous extinction are still being debated by paleontologists. Scientists agree that the main cause of the extinction was a...
seems like it happened so sudden, as geologic time goes, that almost all the dinosaurs
Sutter, John D. “Should scientists ‘Jurassic Park’ extinct species back to life”, www.cnn.com 5 May 2014, 22 May 2014
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Earth has gone through five fully major extinctions before. We currently are in the process of Earth’s sixth mass extinction. This mass extinction is closely related in severity to the extinction of the dinosaurs. Earth’s extinctions are broken into three different areas. The first area was the large number of animals caught by hunter-gathers. The discovery of agriculture led to the second area of extinction, wildlife habitats. These wildlife habitats were destroyed due to humans starting to stay in one area.
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Nowadays it is common to read articles in newspapers and magazines regarding biodiversity issues. Human beings have been knowingly and unknowingly destroying biodiversity since their existence. Biodiversity is the measure of the variety of species of animals living in an area. Forests are usually areas with high biodiversity while deserts are the opposite. Human beings have always destroyed biodiversity either by deforestation, or by some other means. Biodiversity depletion is a natural phenomenon. But the present levels of biodiversity depletion are many times higher than the natural rate. Recently the levels of loss in biodiversity have started causing global concern. Some of the main causes for loss in biodiversity are alteration of habitats, increasing levels of pollution and human population growth.