Earth History

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First found May 22, 2018

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Topic 13
Earth History
Estimated age of the Earth:
• 4.6 billion years
• 4.6 x 109 years
• 4,600,000,000 years
• See ref. tables p. 8
Relative Dating
• Putting events into
order based on when
they occurred.
Vs.
Absolute Dating
• Actual age of the
rock, fossil or event
Relative Dating: Sequence of
Events:
1. 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
2. Folding/ Faulting/ Tilting
• All are younger than the rocks they
appear in.
Drawing:
3. Igneous Intrusions/ Extrusions
• They are younger than the rocks they
intrude into or extrude onto.
Drawings:
4. Internal Characteristics of Rock
A. Sediments are older than the rock in
which they are found.
B. Xenoliths- igneous rocks that contain
pieces of other rocks.
 The pieces are older
C. Veins- mineral veins are younger than
the rocks they form in
5. Unconformities
• Buried erosional surfaces
 Represents a gap in the rock record.
Drawing:
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.
Half-Life
• The amount of time it takes for ½ of a
radioactive isotope to decay.
• 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!!!
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.
Information from Fossils
1.
2.
3.
4.
Types of life
Crustal plate positions
Past environments
Evolution
Index Fossils
• Existed for a short period of time
• Widespread and abundant
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.
Correlation:
•
The process of showing that rock strata
(layers) or geologic events in different places
are the same age.
Techniques for correlation:
1. Direct observation (looking at them!)
2. Similar composition
3. Volcanic ash deposits (cover a large area in a
short time)
4. Index fossils
• Widespread and abundant
• Existed for a short period of geologic time
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