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