Transcript Earth History

Earth History
The Earth is 4.6 billion years old and its
geology has changed greatly with time.
Many of the changes in the past can be
observed in the rock record. Interpreting
the changes in the geology of the earth is
similar to solving a puzzle; we must figure
out how all the pieces fit together.
What events can change the geology of an
area?
Earth History
Principle of Uniformitarianism – “the
present is the key to the past”…in other
words, the processes that can change the
geology today have worked on the rocks in
the past; in a similar manner.
Example: Weathering breaks down limestone
at the same rate today as it did thousands of
years ago. (Weathering rate has not
changed)
Earth History
Absolute Age – the actual age of a rock or
event (can be determined by radioactive
decay of specific elements)
• Some elements decay into other elements
over a specific amount of time (half-life).
ESRT p.1
Practice
A sample with an original amount of 40g of
carbon-14 is found and now contains 2.5g of
carbon-14, how many years old is this sample?
40g
20g
10g
5g
2.5g
This sample has undergone 4 half-lives, and the
half-life of carbon-14 is 5700 years:
5700 yrs. x 4 = 22,800 years!
Earth History
Relative age – The age of rocks or events in
relation to the age of some other rocks or
events. (following a sequence of events)
Earth History
Using Sedimentary Layers to determine
relative age:
Principle of original horizontality
Principle of superposition
Igneous Intrusions
Faults and Folds
Earth History
Principle of original horizontality –
sediments are deposited in horizontal layers
that are parallel to the surface on which they
are deposited.
What does this tell us about tilted or folded
layers of rock?
Earth History
Principle of superposition – in a series of
undisturbed layers, the oldest layer is on the
bottom and each layer above is younger and
younger.
Earth History
Igneous Intrusions – Molten magma forces its
way into cracks in rocks and hardens
(forming an intrusion). Since the rocks
through which the magma moved existed
before the intrusion, these rocks must be older
than the intrusion. (Intrusions are younger!)
Igneous
intrusion
Earth History
Faults and Folds – These features must be
younger than the rock in which they are
found.
Unconformity
unconformity
Erosion wears away rock layers, then more deposition
occurs creating new layer. The unconformity is
the old buried erosional surface. This is also
known as a gap in the rock record.
Put the events in order…
of oldest to youngest
1. _________________
2. _________________
3. _________________
4. _________________
5. _________________
Put the events in order…
of oldest to youngest
1. _________________
2. _________________
3. _________________
4. _________________
5. _________________
6. _________________
7. _________________
8. _________________
9. _________________
Put the events in order…
of oldest to youngest
1. _____________
2. _____________
3. _____________
4. _____________
5. _____________
6. _____________
7. _____________
8. _____________
9. _____________
Putting the sequence together?
Correlation – the process of matching rocks
and geologic events in one location with
rocks and geologic events in other locations.
ESRT page 8-9
ESRT page 8-9
Time Scales:
Eon
Era
Largest
Period
Epoch
Smallest
ESRT page 8-9
What can we find on this page?
ESRT page 3
ESRT page 2
Fossil Record
• Evidence of organisms preserved in the
sedimentary rock record.
• Typically hard shelled organisms or bones
of other organisms are the only evidence
preserved as fossils.
• Organisms must be buried quickly after they
die to be preserved.
Index Fossils
• Used to locate a specific geologic period of
time.
• Abundant and found over large geographic
regions.
• Species lived for a short period of time.
From ESRT page 8-9, identify an index fossil
and the geologic time period it represents.