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The Principle of Uniformitarianism

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The Principle of Uniformitarianism

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    1. The Principle of Uniformitarianism Scientist James Hutton, the author of Theory of the Earth, proposed that geologic processes such as erosion & deposition do not change over time. Uniformitarianism - idea that same geologic processes shaping Earth today have been at work throughout Earths history.

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    3. The Principle of Uniformitarianism, continued Uniformitarianism Versus Catastrophism Huttons theories sparked a scientific debate by suggesting Earth was much older than a few thousand years, as previously thought. A few thousand years was not enough time for the gradual geologic processes that Hutton described to have shaped the planet.

    4. The Principle of Uniformitarianism, continued A Victory for Uniformitarianism Catastrophism was geologys guiding principle until the work of geologist Charles Lyell caused people to reconsider uniformitarianism. Lyell published Principles of Geology in the early 1830s. Armed with Huttons notes and new evidence of his own, Lyell successfully challenged the principle of catastrophism.

    5. Modern Geology -- A Happy Medium Late 20th century, Stephen J. Gould challenged Lyells uniformitarianism. They believed that catastrophes occasionally play important role in shaping Earths history. Today, scientists realize most geologic change is gradual & uniform, but catastrophes that cause geologic change do occur during Earths long history.

    6. Radioactive Decay Absolute dating - any method of measuring the age of an event or object in years. To determine absolute ages of fossils & rocks, scientists analyze isotopes of radioactive elements. Isotopes - Atoms of the same element that have the same number of protons but different numbers of neutrons.

    7. Radioactive Decay, continued Most isotopes are stable, meaning they stay in their original form. Other isotopes are unstable. Scientists call unstable isotopes radioactive.

    8. 8 Radioactive Decay, continued Radioactive isotopes tend to break down into stable isotopes of same or other elements - process called radioactive decay.

    9. Radioactive Decay, continued Because radioactive decay occurs at a steady rate, scientists can use the relative amounts of stable and unstable isotopes present in an object to determine objects age.

    10. 10 Radioactive Decay, continued Dating Rocks How Does It Work? In radioactive decay, an unstable radioactive isotope of one element breaks down into a stable isotope. The stable isotope may be of the same element or of a different element. Unstable radioactive isotope - parent isotope. Stable isotope produced by radioactive decay of parent isotope - daughter isotope.

    11. Radioactive Decay, continued Rate of radioactive decay is constant, so scientists can compare amount of parent material w/amount of daughter material to date rock. The more daughter material there is, the older the rock is. If you know rate of decay for a radioactive element in a rock, you can figure out absolute age of rock.

    12. Radioactive Decay, continued Half-life - the time needed for half of a sample of a radioactive substance to undergo radioactive decay. After every half-life, the amount of parent material decrease by one-half.

    13. 13 Types of Radiometric Dating Scientists use different radiometric-dating methods based on estimated age of an object. There are four main radiometric-dating techniques; youll need to know two. Potassium-Argon Method Potassium-40 has a half-life of 1.3 Gy, & it decays leaving a daughter material of argon. This method is used mainly to date rocks older than 100,000 years.

    14. 14 Types of Radiometric Dating, continued Carbon-14 Method Carbon is normally found in three forms, the stable isotopes carbon-12 & carbon-13, and the radioactive isotope carbon-14. Living plants & animals contain a constant ratio of carbon-14 to carbon-12. Once a plant or animal dies, no new carbon is taken in. The amount of carbon-14 begins to decrease as plant or animal decays.

    15. 15 Types of Radiometric Dating, continued The half-life of carbon-14 is 5,730 years. The carbon-14 method of radiometric dating is used mainly for dating things that lived within the last 50,000 years.

    16. 16 A bit of review!!

    17. Discovering Earths History

    18. Discovering Earths History

    19. Fossils: Defined

    20. Fossils: How Do They Form

    21. Fossils: Altered Remains

    22. Fossils: Trace Fossils

    23. Fossils: Unaltered Remains

    24. Types of Fossilization Makes no sense without caption in bookMakes no sense without caption in book

    25. The Fossil Record

    26. Fossils: Interpreting Past Environments

    27. Depositional Environments

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