1. Earth’s History Review

2. Warm Up – 3/26 AGENDA Turn in Football Time line into tray.
Read pages B9-B15. Take detailed Notes.
Write Q&A on page B15 #1-3.
You will have 15 minutes to complete this warm-up. It is independent work.

3. Earth’s History Planet Earth is approximately 4.5 X 109 years old
Rocks of the crust provide clues to Earth’s past
By analyzing these clues we can infer events from the past

4. Earth’s History Principle of Uniformitarianism
Major assumption in geology
Events in the past occurred the same way that they are occurring today. Examples Include:
Weathering/erosion
Deposition
Volcanism
Plate tectonics

5. Geologic Time
Plate motions and mountain building events can be placed on the geologic time scale

6. Geologic Time A study of the fossil record shows
A great variety of plants, animals, and simpler life forms have lived on Earth in the past
That life forms have evolved through time
Most life forms of the geologic past have become extinct

7. There are two types of Geologic Dating
Absolute
Determines how many years old something is
Relative
Used to determine if one thing is younger or older than another

8. Tools used to determine
Absolute Age
Relative Age
Using radiometric dating
Law of superposition
Use of index fossils
Correlation of rock layers

9. Law of Superposition
Sediments are laid down underwater in horizontal layers and form sedimentary rocks

10. Law of Superposition
In a series of sedimentary rocks the bottom layer is the oldest and the top layer is the youngest
Lower layers must be in place before younger rocks can be deposited on top of them
Exception: when something occurs to overturn layers

11. Grand Canyon

12. Law of Superposition Rock layers are older than folds found in them
Layers were there before they were folded

13. Law of Superposition Rock layers are older than faults found in them
This is logical: you can’t break a rock if it does not exist; so rock containing a fault must be older than the fault

14. Law of Superposition
Fossils are generally the same age as the rock layers in which they are found
Animal remains are deposited along with the sediments that will turn into sedimentary rocks

15. Law of Superposition
Igneous intrusions are younger than the rock that they cut through or flow out of

16. Unconformity
When a new rock layer is formed atop an eroded surface

17. November 18
Fossils
Naturally occurring preserved remains or impressions of living things
Generally only hard parts get preserved
Bones, teeth, shells
Hard parts are replaced by naturally occurring minerals
Allen

18. Fossils Can be a mold (impression) Or a cast Ex: footprint
November 18
Fossils
Can be a mold (impression)
Ex: footprint
Or a cast
Ex: filled in footprint
Allen

19. Fossils (Cont) Other types Ice Tar Carbonaceous film Amber Imprints
Petrified

20. Fossils Why don’t fossils exist in most igneous or metamorphic rock?
November 18
Fossils
Generally found in sedimentary rock layers
Why don’t fossils exist in most igneous or metamorphic rock?
Allen

21. November 18
Fossils
The living organism that made the fossil lived during the time the rock layer was forming
i.e. when the sediment was being deposited
Allen

22. Fossils Fossils can provide information about ancient environments
Marine fossils indicate a marine environment, wooly mammoths indicate a cold environment, etc…

23. Index Fossils Index Fossils--used to date rock layers (strata)
Fossils from creatures that existed for a geologically short period of time
Ex. less than 2.0 x 107
Fossils from creatures that had a wide geographic distribution