1. Topic 13
Earth History

2. Estimated age of the Earth:
4.6 billion years
4.6 x 109 years
4,600,000,000 years
See ref. tables p. 8

3. Putting events into order based on when they occurred. Absolute Dating
Relative Dating
Putting events into order based on when they occurred.
Absolute Dating
Actual age of the rock, fossil or event
Vs.

4. Relative Dating: Sequence of Events:
Law of superposition
The age of the rock increases as you move down the rock column.
Diagram:
Except when the rocks have been overturned or thrust faulted

5. Folding/ Faulting/ Tilting
All are younger than the rocks they appear in.
Drawing:

6. Igneous Intrusions/ Extrusions
They are younger than the rocks they intrude into or extrude onto.
Drawings:

7. Internal Characteristics of Rock
Sediments are older than the rock in which they are found.
Xenoliths- igneous rocks that contain pieces of other rocks.
The pieces are older
Veins- mineral veins are younger than the rocks they form in

9. Unconformities
Buried erosional surfaces
Represents a gap in the rock record.
Drawing:

19. Absolute Dating Radiometric Dating Radioactive Isotope
An isotope of an element that is unstable and breaks down (decays) into another element.
Daughter Product
The stable end product of radioactive decay.

20. Half-Life
The amount of time it takes for ½ of a radioactive isotope to decay.

26. Carbon 14 can only be used to find the age of stuff that is relatively young (50,000 years or less).
NOTHING can change the rate of radioactive decay!!!

27. Fossils: Remains or traces of past life preserved in the rock record.
Fossils usually form from organisms…
That have hard parts
That were buried rapidly.

28. Information from Fossils
Types of life
Crustal plate positions
Past environments
Evolution
Index Fossils
Existed for a short period of time
Widespread and abundant

29. Fossil evidence suggests that a wide variety of plants and animals have lived on Earth and most have become extinct.
An even greater number of organisms were probably never fossilized.

33. Correlation:
The process of showing that rock strata (layers) or geologic events in different places are the same age.
Techniques for correlation:
Direct observation (looking at them!)
Similar composition
Volcanic ash deposits (cover a large area in a short time)
Index fossils
Widespread and abundant
Existed for a short period of geologic time