Mass Extinctions, Then and Now - Assignment Example

Mass Extinctions, Then and Now al Affiliation: Mass Extinctions, Then and Now Mass extinction as a phenomenon remains a topic that has received both criticism and praise, in almost equal measures. The view that mass extinction in itself is an integral part in the process of evolution has elicited an uproar among many, scholars and nonprofessionals. Many scholars have distanced themselves from this view, which was developed during the times of Charles Darwin in the 19th century, dismissing it as being a mere justification of historical theories of extinction such as the biblical story of Noah and the floods which took place wiping out significant amounts of life (Adams, 2010). However, other scholars have taken a keen interest in this view, and have developed volumes of scholarly work that attempt to explain the correlation that exists between the two. This paper will therefore attempt to define mass extinction, examine its effects based on past cases and instances where the phenomenon took place, and create a possibility of a catastrophic event arising from manmade activities that would affect the biodiversity of species. Finally, it would also attempt to paint a future of a world in the event that such a catastrophic situation would occur. What is mass extinction? To better comprehend the term mass extinction, it is paramount that the word extinction is also defined and understood. An organism is said to be extinct when no member of its species exists on earth. This is can be attributed to the fact that not all life is supported on earth. The other reason why a species may go extinct is simply that members of that specie cannot survive given the existing conditions. There are terminologies that have been developed to better understand the concept of extinction, and thus that of mass extinction. These include locally extinct and globally extinct. The former means that members of a certain species are completely unavailable in particular local habitats where they initially would be found. The latter, on the other hand, implies that members of a certain species cannot be traced or found to be existing in any known habitat in the world. There are two types of extinction, namely, background and mass extinction. Background extinction refers to what can be termed as normal extinction. It is a measure of how naturally species go extinct either because not all forms of life can be sustained on planet earth or members of that specie cannot survive. However, the background extinction definition simply touches on the extinction of single species as opposed to multiple species. We will therefore focus on the other type of extinction to address the shortcoming. Mass extinction, also referred to as an extinction event, can be defined as a rapid event which leads to a significant and widespread reduction in the amounts of life on habitable parts of the earth. Therefore, the decline in the diversity and quantity of life on earth must be significant and global, affecting not only species from a certain local habitat, but all forms of life on the universe. As such, the extinction of say the wildebeest in the entire African continent is still viewed as a localized and isolated event. Mass extinction thus occurs only if the event causing extinction is rapid, global in its severity and extent, affecting different forms of life living in different habitats across the earth, and significantly reducing life on earth (Kenneth, 2002). A critique to this definition has also been advanced. Scholars have questioned the two major aspects of the definition, namely the rapidness and the significance of such an extinction event. Issues raised include how to quantify the significance of such an event and how to define the word rapid. Nevertheless, mass extinction events have occurred in the past with profound effects. We will therefore proceed to examine these past mass extinctions, their causes and their effects on biodiversity then. In history, several mass extinctions have occurred across the planet earth. The period in history under review, over which the extinction events have occurred, is that ranging from 500 to 600 million years ago (Tricia, 2007). This is the period where scientists have maintained a record of fossils that were multicellular. However, five instances of mass extinctions have been singled out by scientists. This is by virtue of their intensity and severity to biodiversity. The five have thus been christened the ‘big five’ or simply the five worst mass extinctions. They are the Ordovician – Silurian extinction, the late Devonian extinction, the Permian – Triassic extinction, the end Triassic extinction, and lastly the cretaceous – tertiary extinction (Randy, 2006). The Ordovician – Silurian extinction, also referred to as End Ordovician, occurred between 430 and 450 million years ago. It is categorized as one of the big five, actually secondly placed of the five, because 25 to 29 percent of marine life was lost during that period. The death and subsequent disappearance of marine life during this period is attributed to two major causal events namely a fall in sea levels and glaciations. The formation of glaciers at the time resulted in a drop on water levels at sea exposing marine life to extreme conditions other than those they are used to thus causing death (Sharon, 2011). A rise in the sea level, which resulted from the melting of the glaciers, was also a contributory factor to the significant loss of marine life during the period. The second cataclysmic mass extinction in history is the late Devonian extinction. The causes of this event in history, which is thought to have occurred some 360 million years ago, are not very clear to scientists. However, it is thought that the same causes as those in the end Ordovician, that is drastic and widespread falls in sea level and glaciations, may have resulted in mass extinctions. Falling meteorites are also considered as possible causal agents. The effect of this mass extinction was mostly felt in marine life, as about 21 to 23 percent of marine species were killed. The third extinction event, considered as the worst of the big five, is the Permian – Triassic extinction. The effect of this extinction event was so intense that it has been labeled as the ‘mother of all extinction events’ or ‘the great dying’. During this catastrophic transition, over 95 percent of all earth species were killed, including marine life, vertebrates and insects (Benton, 2003). The causal agents are thought to be volcanic eruptions that led to the death of land vertebrates because of lava flows. In sea, the widespread and significant loss of marine life was because of low, or completely lack of oxygen due to the volcanic activities. The End Triassic, which is also known as the Triassic – Jurassic extinction event, is the fourth of the big five. It is thought to have occurred about 200 million years ago due to volcanic activity that subsequently led to an acute rise in global temperatures and thus global warming. The effect on biodiversity was profound, with 21-23 percent of marine life death and 73 percent of all species going extinct. The last of the cataclysmic events is the cretaceous – tertiary extinction, which is now formally referred to as the cretaceous – paleogene extinction event. There are varying opinions as to what may have caused death and destruction during this transition, with some scientists attributing changes in climatic conditions while others believed the cause to be the impact of falling asteroids. Over 70 percent of all life species were fatally affected, and extinction followed. Having examined five of the earth’s worst mass extinctions, there is need to address the possibility of what is now visibly, a sixth cataclysmic event, or a sixth mass extinction event (Elizabeth, 2014). It is important to note that the five mass extinctions were caused by a combination of both terrestrial and extra terrestrial factors. The terrestrial factors included lack of oxygen, very rapid changes in climatic conditions and changes in sea levels while the extra terrestrial factors include the impact on earth of heavenly bodies such as asteroids and comets. However, the causes of a now possible sixth mass extinction are human in nature (James, 2014). Human induced activities, which are pushing the universe to the brink of another cataclysmic event, can be broadly categorized into five. These are pollution, overpopulation, destruction of habitat, over harvesting, and the invasion of species (Tricia, 2007). Man’s continues destruction of habitat poses the greatest risk to species survival. Pollution and emissions of greenhouse gases such carbon dioxide lead to global warming, as the gases tend to trap the sun’s heat thus raising temperatures. Species, in a bid to survive, will tend to migrate to cooler habitats (Kristi, 2008). However, human induced changes such as massive deforestation to provide room for an overpopulated human species may already have destroyed such cool habitats thus the species will simply die out. Further warming of the atmosphere will lead to reduction of carbon dioxide though the process of weathering. Very low levels of carbon dioxide will eventually lead to an extinction of plant life, as plants are dependent on it for growth. When all plant life ceases to exist, the supply of oxygen in the atmosphere is also grossly affected and will lead to the dying out of multicellular organisms. The impact of such a mass extinction event will be devastative. However, the gradual recovery of species, in line with the theory of evolution, will dictate the future of a post cataclysmic event. Weeds will tend to survive first because they possess the ability to adapt in varying habitats. Other organisms, as in natural selection, will later on diversify due to the changes in climate, and will occupy habitats left bare. The recovery may take over 5 million years after the extinction event (Annalee, 2013). References Adams, J. (2010). Species Richness: Patterns in the Diversity of Life. New York: Springer Science & Business Media Annalee, N. (2013). Scatter, Adapt and Remember: How Humans Will Survive a Mass Extinction. Langridge: Black Incorporated. Benton, M. (2003). When Life Nearly Died: The Greatest Mass Extinction of All Time. London: Thames and Hudson. Elizabeth, K. (2014). The Sixth Extinction: An Unnatural History. New York: Bloomsbury Publishing. James, R. (2014). The Sixth Extinction. London: Orion. Kenneth, G. (2002). Catastrophic Events and Mass Extinctions: Impacts and Beyond. California: Geological society of America. Kristi, L.B. (2008). Species Abundance Changes During Mass Extinction and the Inverse Signor- Lipps Effect: Apparent Abrupt Graptolite Mass Extinction as an Artifact of Sampling. Michigan: ProQuest. Randi, M. (2006). Great Extinctions of the Past. New York: Chelsea House. Sharon, R. (2011). Once and Future Giants: What Ice Age Extinctions Tell Us about the Fate of Earths Largest Animals. London: Oxford University Press. Tricia, A. (2007). Mass Extinction: Examining the Current Crisis. 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