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Understanding Fossils: Types, Preservation, and Their Role in Earth's History

This section explores the fascinating world of fossils, which are the preserved remains of organisms found primarily in sedimentary rocks. Various preservation methods include burial by sediments, amber entrapment, petrification, and freezing. Fossils serve as vital evidence for interpreting Earth’s history, revealing environmental changes and the evolution of life over time. They also help date rock layers using index fossils such as ammonites and trilobites. By studying fossils, scientists gain insights into ancient climates and ecosystems.

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Understanding Fossils: Types, Preservation, and Their Role in Earth's History

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  1. Chapter 3 Section 4 Looking at Fossils

  2. The remains of physical evidence of an organism preserved by geologic processes is called a fossil. • Fossils are mainly in sedimentary rock • Fossils can also be preserved in other materials

  3. Fossils in Rocks • Sometimes when organisms die they are buried by sediments • When the sediments become rock, hard parts of the organism are preserved in the rock

  4. Fossils in Amber • Organisms become trapped in sap • When the sap hardens the organisms are preserved • The hardened sap is called amber

  5. Petrification • Petrification is the process in which minerals replace an organism’s tissues • Permineralization is a process in which the pore space in an organism’s hard tissue (bone or wood) is filled up with mineral • Replacement is a process in which the organism’s tissues are completely replaced by minerals.

  6. Fossils can be found in asphalt • Fossils can be frozen. • In 1999 scientists removed a 20,000 year old woolly mammoth • Cold temps slow down decay. Many frozen fossils are preserved from the last ice age.

  7. Other Types of Fossils • Trace fossils • Mold • Cast

  8. Using Fossils to Interpret the Past • The fossil records only offer a rough sketch of the Earth’s history. • The fossil record is incomplete because most organisms never became fossils.

  9. History of Environmental Changes • The fossil record reveals a history of environmental change • Ex) marine fossils help scientists reconstruct ancient coastlines and the deepening and shallowing of ancient seas • Scientists can reconstruct ancient climates by using fossils

  10. History of Changing Organisms • By studying fossils scientists can interpret how life changed over time • The fossil record is incomplete.

  11. Using Fossils to Date Rocks • Index fossils are fossils of organisms that lived during a relatively short, well-defined geologic time span • Index fossils help scientists date rock layers

  12. Ammonites • To be considered an index fossil the fossils must be found in rock layers throughout the world ex) ammonites • Tropites are a type of ammonites that is similar to a modern squid

  13. Trilobites • Trilobites help date rocks • Paleontologists assume that any rock layer containing a fossil of a trilobite is dated to be about 400 million years old

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