Good Example Of Earth’s Mass Extinctions: The Cretaceous Event Essay

Introduction

This paper would like to discuss the Cretaceous event with the aim of drawing a clear picture of what happened and what caused the extinction of the genera during this time frame or geologic period. In discussing the Cretaceous event, it would be interesting to know the types of species that thrived before the extinction event as well as the types of species that thrived thereafter. Ultimately, it is desirable to determine if there is a connection between climatic changes and the possibility of another extinction event to occur, which is the contemporary concern of the currently thriving species especially the human population. Being the latest of all the known extinction event, the significance of studying the Cretaceous era draws on the remaining geologic and fossil evidence of its existence and its eventual extinction. It should be noted that these extinction events happened several millions of years ago. Understandably, no decisive conclusion can be reached as to what really happened. However, with the use of carbon dating technologies as well as the advancement of man’s knowledge on geological science, scientists began to create highly probable hypothesis as they try to decipher the puzzle of earth’s apocalyptic events.

Five Major Extinction Events

The earth has been home to approximately four billion species in its estimated 4.5 billion years old existence (Barnosky, A., et al., 2011; Dalrymple, B., 1984). Within this time frame, scientists believe that there have been at least five major extinction events; these are the Ordovician event, which ended around 443 million years ago; the Devonian event, which ended at around 359 million years ago; the Permian event, which ended at around 251 million years ago; the Triassic event, which ended around 200 million years ago; and the Cretaceous event, which ended at around 65 million years ago. These extinction events are very significant that it has been used to denote geologic periods. In each of these geologic periods, certain atmospheric conditions occur wherein only a particular genus of organism may thrive. The Cretaceous event, which is the latest of the five major extinction events in history, was believed to have been caused by an extraterrestrial object that have collided with the earth some 65 million years ago, which triggered chaotic terrestrial activities leading to the extinction of the species that thrived during this era.

Cretaceous Era

Fossil evidence of the Cretaceous era has survived and has been a great source of information for scientists who are studying the biological system and geology during this period. Careful scientific examinations of rock formations and these fossils have led scientists to conclude that a particular genus of organisms is thriving in its climatic and ecologic conditions. The Cretaceous period is the final period of the Mesozoic Era, covering the time span of 144 to 65 million years ago. With a mean annual temperature reaching as high as 20˚C, the Cretaceous period was characterized by warm climatic conditions and is considered by most scientists as a greenhouse climate due to the high atmospheric levels of CO2. In line with the warm climate, there was also an increased level of precipitation in high latittudes while precipitation is significantly decreased in lower lattitudes. This precipitation pattern as well as the conducive climate near the poles may have influenced the distribution of vegetation during those era. As observed, there was an increase in vegetation cover in high northern and southern latittudes as the trees and grasses expands towards the poles. Several flora and fauna species emerged under this climatic conditions. In fact, it was during this time when the first flowers bloomed. With the inception of flowers, insects began to emerge perhaps out of the evolution process of some organisms. Most significantly, the earth is roamed and dominated by giant reptiles popularly known as the dynosaurs. Evidence of mammal existence has also been determined although early mammals were not as fully developed as they are today.

The Cretaceous Event

The Cretaceous Event, also known as the Cretaceous and Tertiary (KT) event is considered to be the most violent extinction event the world has ever known. Since the 18th century, theories about extinction events have already been recognized in the scientific community owing to the works of Georges Cuvier, Charles Lyell and Charles Darwin. According to the observation of these notable scientists, certain gaps occur in the fossil records, which suggests that there must be some catastrophic events that may have led to mass extinction of certain species. The dynosaurs were among the most interesting specie that has thrived during the Cretaceous period as evidenced by archeological finds. However, it puzzles scientists on how these gigantic creatures could have been wiped out unless some catastrophic event of collosal nature occurred. Scientists have long hypothesized that extraterrestrial collission may have caused the demise of the dynosaurs as well as other plant and animal species of the Cretaceous period. And so in 1970, a group of scientists led by Luis and Walter Alvarez tried to investigate the amount of cosmic dust that occurred inbetween the Cretaceous and Tertiary period (also known as K-T boundary). As compared to other geological periods, the team found that there was indeed a huge amounts of cosmic debris in the K-T boundary that could only be explained by the impact on earth of an approximately 10 km in diameter meteorite. Years later, the impact site was found after the discovery of the Chicxulub crater in the Yucatan Peninsula of Mexico. The impact of the meteorite as it colided with the earth was apocalyptic in nature. The impact of the speeding 10-Km meteorite would have generated colossal tsunamis in every direction with earthquakes exceeding magnitude 10 on the richter scale. Using computer simulations, scientists theorized that hundreds of gigatons of Sulfur dioxide (SO2) and water vapor produced by the impact may have significantly altered the stratosphere. Also, smoke and dust from the impact may have blocked the sun for several months to years. The dust and fumes from the impact may have been greatly amplified by the eruption of volcanoes that has been triggered by the impact as well. Millions of plants and animals species may have been fatally impacted after the collision while others may have died out of starvation as food source become scarce due to the blocking effect of the dust, watervapor and smoke towards the sun, thereby affecting photosynthesis.

Aftermath of the Cretaceous Event

Dynosaurs became totally extinct as well as other species of animals and plants as a result of the Cretaceous event. It is estimated that 76% of the earth’s species during the time were lost with reptiles and sea creatures suffering the most. Reptiles and other animals may have succumed to the sudden change in temperature as brought about by the blocking reaction of the debris of the collision event. Accordingly, the enormous amount of aerosols and dusts in the atmosphere would have a cooling effect that would have brought the earth’s temperature to near freezing. However, as the enviromental impact of the Cretaceous event subsided, some species began to recover while other species began to emerge. Among the most dominant species to have emerged after the Cretaceous extinction are the mammalian specie. Accordingly, “Paleocene mammals would spread and evolve into the many ecological niches left open by the extinction of the dinosaurs”.

Relation of Global Warming to Extinction Events

Prior to the Cretaceous event, it is quite observable that the extinction events were triggered by extreme changes in climatic conditions. According to studies, each of the five major extinction events has their own probabilistic cause. The Ordovician extinction event, for example, has been triggered by the glacial and interglacial occurrences that may have significantly altered the ecosystem during the time. On the other hand, the Devonian event has been triggered by extremely cold climate followed by a global warming, which could have significantly affected the species survival capabilities. Anoxic water conditions (or the deficient amount of oxygen in water) as well as ocean acidity have been blamed to be the cause of the Permian event, which could have been triggered by volcanic eruptions and global warming. The Triassic event, on the other hand, is believed to have been caused by the elevated carbon dioxide levels in the atmosphere, which triggered global warming and calcification in the oceans. For the same reason, it can be deduced that climatic conditions is indeed a significant factor for the existence and extinction of a particular type of organism.

References

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