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Measuring the History of Earth

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1 Measuring the History of Earth

2 (c) 2007 brainybetty.com ALL RIGHTS RESERVED.
Geologic Time Scale A record of Earth’s history from its origin 4.6 billion years ago to the present Geologists organize Earth’s History by Eons. An eon is the longest span of geological time. (c) 2007 brainybetty.com ALL RIGHTS RESERVED.

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Geologic Time Scale Eon- the largest division of geologic time Era- tens to hundreds of millions of years Period- tens to millions of years Epoch- Hundreds to thousands of years in duration (c) 2007 brainybetty.com ALL RIGHTS RESERVED.

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Relative Age Dating Enables scientists to determine the approximate age of rocks and other objects This is done by comparing past geological events to layers of rock Scientists use the fossil record, & the principle of superposition to date the layers (c) 2007 brainybetty.com ALL RIGHTS RESERVED.

5 The Principle of Superposition
States that rocks and sediment at the bottom of a crust cross section are older than the rocks and sediment that are located at the top of the curst cross section. (c) 2007 brainybetty.com ALL RIGHTS RESERVED.

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Radioactive Decay Radioactive decay: The emission of radioactive particles and the resulting change of their isotopes Half-life: the length of time it takes for one-half of the original isotope to decay (c) 2007 brainybetty.com ALL RIGHTS RESERVED.

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Dating Rocks Radiometric dating is used to determine the age of igneous and metamorphic rocks Done by determining the relative portions of particular radioactive isotopes that are present in a sample Why is radiometric dating not used for sedimentary rocks?(What’s different about sedimentary rock?) (c) 2007 brainybetty.com ALL RIGHTS RESERVED.

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Carbon Dating Used to determine the age of ORGANIC materials Uses the half-life of Carbon -14 Carbon-14 has a much shorter half-life than other radioactive isotopes (c) 2007 brainybetty.com ALL RIGHTS RESERVED.

9 Carbon Dating: How it works
Tissues of all living things contain C-14 During an organisms life the C-14 decays, but is replenished by respiration When the organism dies it no longer takes in C-14. Scientists measure the amount of C-14 in organic matter to see how much time has passed. (c) 2007 brainybetty.com ALL RIGHTS RESERVED.

10 Other ways to determine absolute age
Tree Rings: growth rings of trees are matched to determine chronology of trees Ice Cores: contain records of past environmental conditions in annual layers of snow depositions Used to determine glacial cycles & climate change (c) 2007 brainybetty.com ALL RIGHTS RESERVED.


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