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Fossilization is a rare phenomenon that preserves remains or traces of ancient organisms, such as mineralized bones, footprints, and sometimes soft body parts. The process occurs over millions of years, transforming organic materials into rock-like structures as minerals seep in. In paleoanthropology, fossils provide critical data for understanding human evolution, estimated to trace back 4-6 million years. Various dating techniques, including relative and chronometric methods, help determine the age of these fossils, though limitations exist, especially for older samples.
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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
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
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)
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
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
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)
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
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
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
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
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
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#
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.
