Earth Science 3.4<br />Looking at Fossils<br />
Describe five ways that different types of fossils form.<br />List three types of fossils that are not part of organisms.<...
Fossilized Organisms<br />Fossil<br />The trace or remains of an organism that lived long ago, most commonly preserved in ...
Fossils in Amber<br />Organisms occasionally become trapped in soft, sticky tree sap, which hardens and becomes amber.<br ...
Fossils in Asphalt <br />There are places where asphalt wells up at the Earth’s surface. These thick, sticky pools can tra...
Other Types of Fossils<br />Trace Fossils<br />Naturally preserved evidence of animal activity<br />Examples:<br />Preserv...
Using Fossils to Interpret the Past<br />The Information in the Fossil Record<br />Offers only a rough sketch of the histo...
Using Fossils to Date Rocks<br />Scientists have learned that particular types of fossils appear only in certain layers of...
Ammonites<br />Tropites,a marine mollusk similar to a modern squid, lived between 230 million and 208 million years ago.<b...
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Earth Science 3.4 : Looking at Fossils

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Earth Science 3.4 : Looking at Fossils

  1. 1. Earth Science 3.4<br />Looking at Fossils<br />
  2. 2. Describe five ways that different types of fossils form.<br />List three types of fossils that are not part of organisms.<br />Explain how fossils can be used to determine the history of changes in environments and organisms.<br />Explain how index fossils can be used to date rock layers.<br />Objectives:<br />
  3. 3. Fossilized Organisms<br />Fossil<br />The trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock.<br />Most often preserved in sedimentary rock, but other materials can also preserve evidence of past life.<br />Fossils in Rocks<br />When an organism dies, it either begins to decay or is consumed by other organisms. Sometimes dead organisms are quickly buried by sediment, which slows down decay.<br />Shells and bones are more resistant to decay than soft tissues, so when sediments become rock, the harder structures are more commonly preserved.<br />
  4. 4. Fossils in Amber<br />Organisms occasionally become trapped in soft, sticky tree sap, which hardens and becomes amber.<br />Insect fossils have often been preserved in this way, but frogs and lizards have also been found in amber.<br />Petrifaction <br />Process in which minerals replace and organism’s tissues.<br />Permineralization<br />Process in which the pore space in an organism’s hard tissue is filled up with mineral.<br />Replacement<br />Process in which an organism’s tissues are completely replaced by minerals.<br />
  5. 5. Fossils in Asphalt <br />There are places where asphalt wells up at the Earth’s surface. These thick, sticky pools can trap and preserve organisms.<br />Frozen Fossils<br />Since cold temperatures slow down decay, many types of fossils have been found preserved in ice.<br />
  6. 6. Other Types of Fossils<br />Trace Fossils<br />Naturally preserved evidence of animal activity<br />Examples:<br />Preserved animal tracks<br />Preserved burrows or shelters that were made by animals<br />Coprolite, which is preserved animal dung.<br />Molds and Casts are two more examples of fossils.<br />Mold<br />mark or cavity made in a sedimentary surface by a shell or other body.<br />Cast<br />type of fossil that forms when sediments fill the cavity left by a decomposed organism.<br />
  7. 7. Using Fossils to Interpret the Past<br />The Information in the Fossil Record<br />Offers only a rough sketch of the history of life on Earth. <br />Incomplete because most organisms never became fossils.<br />Scientists know more information about organisms that had hard body parts and that lived in environments that favored fossilization.<br />History of Environmental Changes<br />The fossil record reveals changes in an area’s climate over time.<br />By using the fossils of plants and land animals, scientists can reconstruct past climates.<br />History of Changing Organisms<br />By studying the relationships between fossils, scientists can interpret how life has changed over time.<br />
  8. 8. Using Fossils to Date Rocks<br />Scientists have learned that particular types of fossils appear only in certain layers of rock.<br />By dating the rock layers above and below these fossils<br />Scientists can determine the time span in which the organisms that formed the fossils lived.<br />If a type of organism existed for only a short period of time, its fossils would show up in a limited range of rock layers.<br />These fossils are called index fossils.<br />Index fossils<br />Found in the rock layers of only one geologic age, and can be used to establish the age of the rock layers.<br />
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  10. 10. Ammonites<br />Tropites,a marine mollusk similar to a modern squid, lived between 230 million and 208 million years ago.<br />Trilobites<br />Fossils of a genus of trilobites called Phacopsare another example of an index fossil.<br />Trilobites are extinct and lived approximately 400 million years ago.<br />When scientists find Phacops in a rock, they assume that the rock is approximately 400 million years old.<br />

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