1. Earth’s History in Stone

2. A. evidence of organisms that lived long ago.
I. Fossils
A. evidence of organisms that lived long ago.
B. Fossils are found in layers of sedimentary rock. The organism is buried in mud, sand, or clay which hardens with time into rock.

3. II. Types of Fossils

4. A. Trace Fossils Marks left by an organism
Ex. Footprints, snake trail…….

5. B. Mold Fossils
An organism is buried in sediment and decays to form an empty space
Ex. Mold of snails, clams………

6. C. Cast Fossils
The mold, once hardened, fills with minerals that form a replica of the original organism
Ex. Sea star, snail…….

7. D. Imprint Fossils
A thin organism, such as a leaf, leaves behind a Carbon imprint in the rock as it decays
Ex. Fern, leaf, pine needle…….

8. E. Petrified Fossils The tissue is slowly replaced by minerals
Ex. Petrified wood…….

9. F. Preserved Materials Fossils
The original material, usually hard tissues, is still contained in the fossil.
Ex. Bones, teeth, insects in amber…….

10. III. What do Fossils Tell US?
Size of the organism
Behaviors of the organisms
Climate in the area
Age of the material

11. IV. Dating Fossils Relative Dating – B. Radiometric Dating –
- Older layers are on the bottom/younger
layers on the top
- uses index fossils of known ages
B. Radiometric Dating –
-Uses radiometric isotopes and half lives
to determine age

12. A few Radioactive Isotopes and their Half-Lives