Chapter 25

Chapter 25 - Chapter 25 The History of Life on Earth 25.1...

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Chapter 25: The History of Life on Earth 25.1 – How do scientists date ancient events? o Plant and animal breeding by agriculturalists is an example of short term evolution o Long term evolution is hard to analyze as ongoing change, we need to look at things like fossils o Fossils are the preserved remains of ancient organisms o They tell us about the body form – morphology – or organisms o Earth’s history is mostly in its rocks, the oldest strata, or layers, of rock are sedimentary rock o Sedimentary rock is formed at the bottom of oceans due to falling sediment o Geologists looking at sedimentary fossils came to 3 conclusions Fossils of similar organisms are found in widely separated parts of the earth Certain fossils are found in younger rocks, while certain fossils are found in older Organism fossils found in higher, more recent strata of rocks are more similar to modern organisms than those found in lower, more ancient strata o Radioisotopes give us a way to measure the absolute age of rocks o Radioactive isotopes of elements have rates of decay called half lives o Using the information about the exponential decay of radioactive isotopes, we are able to find the age of certain rocks o The reason this isn’t always accurate is because sedimentary rocks are formed from materials that existed for varying lengths of time before being transported o Therefore, igneous rocks formed from volcanic activity would be more accurate o Potassium 40 and argon 40 are used to date rocks adjacent to sedimentary rocks o Radioisotope dating of rocks combined with fossil analysis is the best way to
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This note was uploaded on 09/08/2011 for the course LS 1 taught by Professor Thomas during the Summer '05 term at UCLA.

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Chapter 25 - Chapter 25 The History of Life on Earth 25.1...

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