12.1 The Fossil Record
1. Form in Several Ways (The following are some of the processes that make fossils.)
a. Permineralization minerals carried by water are deposited around a hard structure (may replace the hard structure) The most common fossils result from this process. A1. Natural Casts form by water removing the bone/tissue, leaving an impression in sediment. Minerals fill in the mold, recreating the original shape of the organism A2. Trace fossils record activity of an organism. Ex. nests, burrows, Imprints, footprints A3. Amber-preserved fossils are organisms that become trapped in tree resin that hardens into amber after the tree gets buried underground A4. Preserved remains form when an entire organism becomes encased in material such as ice or volcanic ash or immersed in bogs. b. Most fossils form in sedimentary rock (layers of sediment). The best environments for fossilization include wetlands, bogs, and where sediment is continuously deposited Ex. river mouths, lakebeds, and floodplains c. For Permineralization, the organism must be buried or encased in some type of material (sand, sediment, mud, tar) soon after death while the organism’s features are still intact. Then groundwater trickles into tiny pores and spaces. The excess minerals in the water are deposited on the remaining tissues. The mineral deposits are left behind making a fossilized record to replace the organic tissues with hard minerals. It has the same shape as the original structure and may keep tissue. 2. Radiometric Dating Provides an Accurate Estimate of a Fossil’s Age.
a. Relative Dating estimates the time during which an organism lived. It’s done by comparing the placement of fossils of that organism with the placement of fossils in other layers of rock.
b. Radiometric Dating is a technique that uses the natural decay rate of unstable isotopes found in materials in order to calculate the age of that material. (Done to calculate actual age of Fossil)
c. Isotopes are...
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