BIO108 - BIOL108 Written Assignment#2 Samuel Mooney...

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BIOL108 Written Assignment #2 Samuel Mooney 41450345 The sixth great wave of extinction Our planet is the product of millions of years of geological and biological processes that have led to the development of a huge range of diversity within both the geological (hydrosphere and lithosphere) and biotic (biosphere) realms of Earth. The Earth is the sum of the relationships between these ‘spheres’ - which are again, rooted in millions of years of change and evolution. All life on earth simultaneously contributes to, and relies upon these relationships, a delicate balance that makes this planet conducive to the myriad of different forms of life we see today. More diversity exists on earth at present than at any other time in its entire history (Dirzo & Raven, 2003; Williams, 2000). However, there are major concerns that this diversity is under serious threat, and that the planet is facing a mass extinction of species largely different to any ever witnessed in prehistory (Brooks et al ., 2002; Chivian, 2001; Dirzo & Raven, 2003; Hughes, 2004; Mader, 2003; Myers, 2001; Rosenzweig, 2005). Over time, life on Earth has followed an evolutionary, upward trajectory toward greater diversity of species (Sole & Newman, 2002). The present level of marine diversity is estimated to be twice its average over the past 600 million years, and that of terrestrial diversity is also twice its historical average since organisms first Throughout the planet’s history, evolution of the Earth has been punctuated by a number of major interruptions, known as “mass extinctions”, as a result of which a large portion of species have been permanently eliminated (Dirzo & Raven, 2003; Williams, 2000). A mass extinction can be defined as an exceptional decline in biodiversity that is substantial in size and generally global in extent, and affecting a broad range of taxonomic groups over a short period of time (Mader, 2003; Myers, 2001). In the prehistoric past, the five greatest mass extinctions are said to have 1
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BIOL108 Written Assignment #2 Samuel Mooney 41450345 occurred at the final Ordovician period (approximately 435 million years ago), the late Devonian period (357 million years ago), the final Permian period (250 million years ago), the late Triassic period (198 million years ago), and the final Cretaceous period (65 million years ago) (Eldridge, 2005; Mader, 2003; mass extinction, 2005). These are believed to have been caused by large meteorite impacts, and/or major
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This note was uploaded on 12/14/2008 for the course BIOL 108 taught by Professor Gillings during the Spring '07 term at San Diego.

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BIO108 - BIOL108 Written Assignment#2 Samuel Mooney...

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