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  1. Record of Time

  2. The Nature of Fossils • fossilization is a rare phenomenon • can be any remains or traces of ancient organisms • mineralized bones (most common) • footprints • soft body parts 165 million years ago

  3. process • bones are composed of inorganic minerals and organic molecules • most of the organic components are consumed by bacteria after death • water infused with minerals seep into the bone and replace chemicals in the bone with rock-like minerals Mineralization of bone underground

  4. cannot use the criteria of reproduction to distinguish species when we only have skeletal remains • the data for paleoanthropology is found mainly in the fossil record • earliest human whose DNA has been studied was much less than 100,000 years old (hominin evolution goes back 4-6 million years)

  5. Overview of DatingRelative dating • simply tell us that one thing is older or younger than another • they do not tell us when an event happened

  6. Relative Techniques • stratigraphy , or stratigraphic dating • with layers of deposits, those laid down first will be on the bottom and those laid down last will be on the top

  7. fluorine analysis • primarily used for verifying whether or not two fossils in the same strata at a site were in fact from the same animal • Piltdown Man Hoax (7:24)

  8. biostratigraphy • when the bones of our early ancestors are found in the same strata (layer) as those of other animals that are known to have lived only during a specific time period in the past, we assume that these ancestors must also have come from that time

  9. Chronometric dating • place events in their chronological position with reference to a universal time scale such as a calendar • written record and tree ring data are the most accurate • unfortunately, only can go back 5,000-10,000 years

  10. most techniques (at least 10) are based on the rate of changes in atoms resulting from radioactivity • the decay of radioactive elements occurs at different rates, depending on the isotope 

  11. Chronometric Techniques • Radiocarbon Dating (also called carbon-14 and C-14 dating) • Carbon dating (2:10) • upper limit is about 50,000 years • the atmosphere is bombarded by radiation, nitrogen is broken down into an unstable isotope of carbon - carbon 14 (C-14) • becomes attached to organic molecules through photosynthesis in plants and becomes part of their molecular makeup • process of ingesting C-14 continues as long as the plant or animal remains alive

  12. rate of decay are stated in terms of half-lives • one half-life is the amount of time required for ½ of the original atoms in a sample to decay • the decay, of nuclei provides us with a reliable clock that is unaffected by normal forces in nature • rate will not be changed by intense heat, cold, pressure, or moisture

  13. How Carbon-14 Dating Works (1:07) • when the organism dies, the ratio of C-14 within its carcass begins to gradually decrease • rate of decrease is 1/2 the quantity at death every 5,730 years. That is the half-life of C-14 • The Shroud of Christ(9:32 min total) • http://www.pbs.org/wnet/secrets/previous_seasons/lessons/lp_shroud_videos.html#

  14. Potassium-Argon Dating • provide dates for much older sites than those datable by radiocarbon dating • half-life of potassium-40 is approximately 1.25 billion years.