evolution

evolution - Alan Richardson 2 The theory of evolution...

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© Alan Richardson
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The theory of evolution offers an explanation for the existence of all living organisms on the Earth today and in the past It supposes that present day organisms have all been derived from organisms that lived in the past By a series of very small changes over millions of years new species have developed from previous species* Over a period of about 3000 million years, many new species have been produced and many have become extinct. We know a great deal about the organisms that lived millions of years ago from studying their fossilised remains. 2
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There are many ways in which an organism can be fossilised One of these ways is shown in the next sequence of slides In principle, a fossil is formed when an organism dies, its body is enclosed in mud, or sand. The soft parts decay but some of the hard parts (skeleton, shells, seeds) are preserved The mud or sand eventually becomes rock and the hard parts of the organism are mineralised. When the rock is exposed as a result of earth movements or erosion, the fossil remains can be dug out and studied. 3 Fossil formation
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Living fish A Dies Enclosed in sediment Hard parts fossilised Living fish B Dies Enclosed in sediment Hard parts fossilised Fish B becomes a fossil much later than fish A The sediment eventually becomes rock The deeper the rock layer, the older the fossil 4
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living fish sediment from river fish skeleton partly buried by sediment 5
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fish skeleton fossilised older sediment becomes rock more recent sediment collects 6
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land raised above water level recent rock older rock 7
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earth movements fracture rock fossilised skeleton exposed 8
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When rock strata become exposed, it can be assumed that, in most cases, the lowest layers are the oldest* This means that the fossils of organisms preserved in the lowest layers represent animals and plants that lived many millions of years ago rock strata of increasing age 9 © Alan Richardson
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© Alan Richardson This is a fossil of a fish which lived 40 million years ago 10
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This is a reconstruction, from fossil remains, of an ‘armour-plated’ fish which lived 350 million years ago dorsal fin The fish which gave rise to fossils such as this, were very different from today’s fish 11
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This note was uploaded on 11/29/2011 for the course BIO 218 taught by Professor Young during the Fall '11 term at BYU.

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evolution - Alan Richardson 2 The theory of evolution...

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