1. FOSSILS

2. help geologists study Earth’s past & determine…
Fossils
help geologists study Earth’s past & determine…
Approximately when life began
What plants & animals were 1st to live on land
When organisms appeared/disappeared
How organisms live

3. Fossils
Can be in the form of:
REMAINS
IMPRINTS
BONES
TEETH
TRACES

4. How Fossils form The body must be protected from scavengers & bacteria
Hard parts have a better chance of becoming fossils
Fossils are found in sedimentary rocks

5. Types of Fossils Original remains Petrified remains Molds/Casts
Trace fossils
Carbonaceous film

6. Original Remains An actual organism or part of an organism
Usually forms in amber or ice – must be preserved quickly

7. Carbon residue left by an organism
Carbonaceous Film
Carbon residue left by an organism
Coal is a carbon residue left by millions of organisms together – a fossil fuel!

8. Replaced or Petrified remains
Some or all of the original material has been replaced by minerals, such as when silica seeps into buried trees & creates a replica of the tree called petrified wood

9. Molds & Casts Impressions of an organism left in clay, sand or mud
Mold: organism decays inside rock, leaving a cavity that is an impression of the outside
Cast: mold fills in with sediments, making a replica of the organism
Watch them form!
Cast
Mold

11. Trace Fossils
Fossilized tracks, tools, burrows or other traces left of ancient organisms

12. INDEX FOSSILS
Since each organism comes from a specific time period, we can use a fossil to determine the age of the rock it is found in. The shorter the time a certain organism lived, the better we know when the rock formed. These special fossils are called index fossils.

13. Index Fossils - Requirements
Existing for a short period of time
Abundant over a wide area
So it is more useful for comparing rocks in different places

14. Which of the following do you think is most likely to preserve a fossil safely, & why?

15. State Fossils Delaware: Belemnitella americana
Virginia: Chesapecten jeffersonius
Maryland: Ecphora gardnerae

16. Bibliography http://wrgis.wr.usgs.gov/docs/parks/gtime/