1.Fossils Chapter 21

2. Fossils

Remains or traces of once living organisms

Tells scientists when, where and how organism lived

Formation

• Normal- Organism decays (deer on road)

• MUST keep organism from rotting

• • Quick burial (sand, mud, tree sap, etc)

• • Hard parts (bones, wood, etc)

3. Types 4. Petrified Remains

Hard, rock-like parts replaced by mineral (calcium)

Bones, Tree trunks

5. Carbonaceous Film

Carbon Deposits

Coal, oil, Natural gas

6. Molds and Casts

Remains Covered

Sediments Harden

Water dissolves object

Mold Remains

Cast- Sediment fills mold and hardens

7. Original Remains

Entire (or part) of organism is preserved

Amber (Tree Sap), Ice, Bog (swamp)

8. Trace Fossils

Not actually the remains of the organism, but evidence it has been there

Footprints, Burroughs, etc

9. How do we figure out age??

Absolute Age-Exact age

• Example 3412 years old or 15 years old

Relative Age- Approximate Age

10. Relative Age

Best guess of age

Index Fossils- Fossils from species that lived for short periods of time and were wide spread across the world

Rock Layers-

• Law of Superposition- above position

• • In UNDISTURBED layers of rocks, the oldest layers are on the bottom and younger layers on top

• • Think about a clothes hamper

11. Geode 12. Absolute Dating

True Age

Radioactive Decay- Breakdown of unstable isotopes into stable atoms

Isotope- Variation in number of neutrons in an atoms nucleus

Carbon- 2 isotopes

• C 12 - 6p and 6 n=12

• C 14 - 6p and 8n=14

• C 14is unstable

13. Radiation

Alpha ( )- blocked by newspaper

• 2(p + )&2n=mass# decrease by 4, atomic # decrease by 2

Beta ( )- Blocked by brick wall

• 1 e -=no change in mass #

• Electronis from neutron (p& e - )causing Atomic # to increase by 1

Gamma ( ) Blocked only by lead!

• Photon

14. Isotopes

Unstable- Parent isotope

Stable- Daughter

15. Half-Life

Amount of time needed to breakdown half of the parent material into daughter material

Carbon 14- 5730 years

Uranium- 4.5 billion years

Potassium 40- 1.3 billion years

Which would you use to date the planet?