Humans Causing The Worlds Sixth Mass Extinction Biology Essay


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Humans could be causing the sixth mass extinction of the world through the effect the human species has on the planet earth. Human population density increases, climate change due to human activities and increased human exploration and interference of nature are some of the ways humans are on their way to causing the sixth mass extinction. A mass extinction refers to "the extinction of a significant proportion of the world's biota in a geologically insignificant period of time" (Hallam & Wignall, 2002, p. 2). Put simply this means a large amount of species die out a little amount of time. Raup (1992) suggests that approximately half the earth's surface must be environmentally affected in order for a mass extinction, on par with previous mass extinctions, to occur (Hallam & Wignall, 2002).

Previous mass extinctions have occurred towards the ends of the Ordovician, Devonian, Permian, Triassic and Cretaceous eras (Mader, 2008). These time periods show a sudden marked decrease in biodiversity. Towards the end of the Ordovician period, the climate turned cold and it is believed up to 85% of the earth's species disappeared. These species would have consisted of trilobites and brachiopods. The late Devonian mass extinction which was only recently recognised as a mass extinction in the late 1960's, continued for 20-25 million years with several extinction events such as the Kellwasser and Hangenberg (Hallam & Wignall, 2002). Species including sponges, calcareous algae, foraminifera and bivalves suffered extinction within this period (Hallam & Wignall, 2002). The mass extinction of the late Permian era over 250 million years ago is known to be the most severe with extinction of 54% of marine families and 96% of all marine species (Erwin, 1990). During the Triassic period, plant life consisted mainly of confiers and cycads. It was during this time period the first dinosaurs appeared and continued to survive despite a significant decrease in biota towards the end of this era. It is believed that the Cretaceous mass extinction was caused by meteorites that fell to the earth causing a dust cloud. This dust cloud then blocked out the sun, causing atmospheric temperatures to drop and the majority of life on earth to cease. The Creataceous mass extinction marked the extinction of the dinosaurs (Mader, 2008).

The sheer increase in human population and density has affected the earth's animals. It is estimated that the world population grows at approximately 1.15% per year. Within the 40 years between 1959 and 1999, the world population doubled from 3 billion to 6 billion (, 2009). This translates to not only an increased strain on natural resources such as water but also increased competition for resources amongst all living things. Human activity has had a tremendous impact on the planet earth. It is estimated between one third and one half of the earth's surface has been altered by human activities such as deforestation, forestry and development (Vitousek, Mooney, Lubchenco, & Melillo, 1997). These practices alter the earth's biodiversity and drive climate change affecting ecosystems which consequently causes disruption to the animal kingdom. Land transformation also directly contributes to climate change with an approximate 20% increased concentration of greenhouse gases and air pollution (Vitousek, Mooney, Lubchenco, & Melillo, 1997). Within the oceans, although the impact of human activity can be difficult to measure, there is significant damage. It is estimated 50% of the world's mangroves have been destroyed or severely affected by humans (Vitousek, Mooney, Lubchenco, & Melillo, 1997). Needless to say, every area of the planet that is affected by humans, affects every living thing surviving within that area.

There have been many animals that have existed and become extinct before humans have even discovered they may have once existed at all (Jefferson & Zuckerman, 1993). Coupled with the arrival of the first British settlers to Australia came the disappearance of nearly all large mammals and flightless birds (Jefferson & Zuckerman, 1993). The largest animal types have suffered extinction such as the Dodo, the elephant birds of Madagascar and the turtles of Galapagos. A predicted 13 000 turtles disappeared within the Galapagos islands between 1838 and 1888 due to their demand as a food supply on crew ships crossing the area (Jefferson & Zuckerman, 1993). Such instances of animal extinction due to humans are increasingly common. Recent calculations show that animal extinction has increased by 100 to 1000 times since human domination of the planet (Jefferson & Zuckerman, 1993). This translates into approximately 18% of mammals, 11% of birds, 5% of fish and 8% of flora on earth threatened with extinction due to human domination (Jefferson & Zuckerman, 1993).

Although there are countless specific examples of particular species that have become extinct due to reasons directly related to human activity, the extinction of earth's megafauna is the most poignant. The extinction of the megafauna, land animals weighing up to 45kg, has been attributed to human colonisation (Roberts, et al., 2001). Megafauna extinction in Australia occurred within the last million years, directly after known human settlement. This extinction pattern continued for North then South America, Madagascar and New Zealand providing evidence to suggest human colonisation could have contributed to the extinction of the megafauna (Roberts, et al., 2001).

Humans are causing the sixth mass extinction through continued development to advance the human race without consideration of the environmental impact (Eldredge, 2001). It is predicted three major causes of animal extinction are direct habitat destruction, over exploitation and introduced species. Human consumption and exploitation of natural resources causes changes in the earth's atmosphere such as an increase in greenhouse gases leading to increased temperatures on earth.

Humans are causing the sixth mass extinction through consumption of natural resources that has a significant impact on the earth's flora and fauna. Extinction rates of animals have dramatically increased since human colonisation and will continue to decrease without strict measures of conservation by all.

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