1. Geologic Time 1

2. (Answer on a Lecture Note Page)
What Happened First?
(Answer on a Lecture Note Page) 2

3. Preserved remains of ancient life
Fossil
Preserved remains of ancient life
Found mostly in sedimentary rock
Never in igneous rock 3

4. Body is covered by sediment (quickly...days)
Formed
(usually)
An organism dies
Body is covered by sediment (quickly...days)
Slowly hardens into a fossil
Fleshy parts decay
Hard parts leave fossils 4

5. Molds & casts Mold is hollow area left after organism finally decays
Example 1:
Molds & casts
Mold is hollow area left after organism finally decays
Cast is when mineral deposits fill the mold, creating a copy 5

6. 6

7. Example 2:
Carbon Film
Thin coating of carbon left behind on a rock 7

8. Trace Fossils Show evidence of activity Not the organism itself
Example 3:
Trace Fossils
Show evidence of activity
Not the organism itself
Footprints
burrows 8

9. Provide evidence of how life has changed over time
Fossil record
Provide evidence of how life has changed over time
Older fossils (found deeper) have simplest structure.
Give clues to past environments 9

10. Supports the theory of evolution Remains of many extinct species10

11. Relative age Finding age of rocks Absolute age
Older or younger than other rocks
Absolute age
How old it is since formation 11

12. Look at rock layers Relative age Those on bottom formed first
Each layer on top is newer than the one below it
“Law of Superposition”
“Law of Original Horizontality”
Layers get deposited “flat” 12

13. Look at Faults Crack in the Earth’s surface
Layers do not line up anymore
Fault is younger than the rock it splits 13

14. 14

15. Look at Igneous rock layers Extrusion – layer of lava
Younger than rock below it
Intrusion – pocket of magma pushed into other rocks layers
Younger than rock below & around it 15

16. Unconformity – gap in the geologic time record
Missing part of the rock from erosion 16

17. 17

18. Use index fossils Certain fossils occur all over
For short period of time
Example: trilobites
Find index fossil tell relative ages of rock layers for different areas of the world 18

19. 19

20. 20

21. Geologic Sequence Example