1. Quick-write What is a fossil?

2. Fossils Fossils are remains, or evidence, of living organisms that have been preserved over millions of years.

3. Rock fossils Remains of living organisms that have been turned into rock. The hard parts of the organism like shells and bones get buried in sediment. Found in layers of sedimentary rock.

4. Molds and Casts

5. Petrified wood

6. Trace fossils Evidence the organism existed is preserved in rock. Examples include: footprints, animal homes or even feces.

7. Carbon films Every living thing contains carbon. Sometimes when an organism dies the carbon is left behind on a rock in a visible layer.

8. Original remains These are fossils that are actual bodies or parts of bodies of the organism. They are preserved by being sealed inside of a substance that keeps the organisms from decaying.  Amber (resin or tree sap)  Ice (freezes the dead organism)  Tar (sticky, oily substance)

10. Index Fossils Some fossils can be used as index fossils to provide information about the age of rock layers. Not all fossils are index fossils. An index fossil must have lived: 1.For a relatively short period of time 2.In many places around the world

11. Index Fossils For example: Viviparus is a common river snail that has only been around since the late Jurassic period. Rocks containing fossils of Viviparus are younger than the late Jurassic period.

12. Relative Age Relative age is the age of an event or object in relation to other events or objects. For example I have a younger brother, so you know he is less than 42 but you don’t know his exact age. If a scientist finds a new kind of fossil in the same rock as a Viviparus fossil he can determine the relative age of the new fossil.

13. Rock layers and relative age

14. Absolute Age To know my brothers absolute age you would have to know is birthday. Scientists can find out the absolute age of rocks and fossils they use a technique called radioactive dating. Uranium 235 can be used to date igneous rocks Carbon 14 is used to date anything that was living.

15. Radioactive Dating When a rock or living organism is formed some of its elements are unstable. Depending upon the element, over a period of time the element undergoes radio active decay at a constant rate. This decay can be measured in “half-life” which is the time it takes for half of the element to decay.

16. Carbon 14 Decay