1. Fossils, Strata and Dating
What is it, where did it come from, how old is it?

2. I. Law of Uniformity =
Processes that we observe working on the Earth today are the same as those that were working in the past.
same process
same speed
Plates move
Rock erodes
Sediment deposits & forms sedimentary rock
volcanoes create igneous rock

3. Relative Dating video

4. II. Relative Dating uses Strata (layers)
A. Principles:
1. original horizontality –
sedimentary layers start out horizontal
(bcs sediment deposits bit by bit on ocean/lake bottom)
2. superposition –
oldest sedimentary layers
on bottom
3. crosscutting –
things that cut horizontal layers
are newer than the layers

5. Horizontality, Superposition, Crosscutting

6. III. Absolute Dating A. Based on half life
1. how long it takes for half
of the atoms to decay
B. Each isotope decays at a different speed
C. The amount of remaining tells us
how long something has been around

7. To estimate the age of a rock find percent of U-235 remaining read graph

8. If no U-235 remaining try a different isotope

9. IV. Fossils A. Preserved remains organisms B. Form in sedimentary rock
C. most no longer have organic material (no C-14)
D. age of fossils that lack Carbon determined by
1. relative dating of sediment layers
2. radiometric dating of volcanic ash/rock nearby
start at 2:00

11. V. Types of Fossils
A. cast = buried body decays and is replaced by sediment
B. mold = imprint of body
C. mineralization = minerals seep into a buried bone/tooth
gradually replace organic materials
D. unaltered = still bone..trapped in tar pit or ice or amber

12. Types of fossils Web site

13. bracketing
ime/froshlec9.html