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The Fossil Record Chapter 19
Fossils and Ancient Life • Fossil = Preserved remains of an organism or evidence of the presence of an organism • Types of Fossils: • Preserved body structures • Skeleton • Teeth or jawbones • Pieces of a leaf • Trace fossils • leaf imprints • Tracks • Burrows • droppings
Where Fossils Are Found Most fossils are found in sedimentary rocks • Small bits of sand, silt, or clay settle to the bottom of a body of water • As sediments build up, organisms or traces of organisms are buried • Soft structures decay quickly and hard structures can be preserved • Layers of sediment continue to build up over time and remains are buried deeper and deeper then compressed
What Fossils Can Reveal • The fossil record is incomplete, but contains information about ancient life. • Paleontologists study fossils for clues • Structure of ancient organisms, their environment, and how they lived
Dating Earth’s History Scientists use different methods to determine a fossil’s age. • Relative Dating • Index fossils = easily recognized fossil species. • The deeper a fossil is found, the older it is • Radiometric Dating • Determining a fossil’s age • Uses radioactive elements and the rates at which they decay
Geologic Time Scale • Organized into Eras • Eras are divided into periods