Download Continuity of Cause and Effect

Geologic Time
and Earth
History
Two Conceptions of Earth History:
Catastrophism
 Assumption: Great Effects Require Great
Causes
 Earth History Dominated by Violent Events
Uniformitarianism
 Assumption: We Can Use Cause And Effect to
Determine Causes of Past Events
 Finding: Earth History Dominated by Smallscale Events Typical of the Present.
 Catastrophes Do Happen But Are Uncommon
Uniformitarianism
Continuity of Cause and Effect
 Apply Cause and Effect to Future Prediction
 Apply Cause and Effect to Present Technology
 Apply Cause and Effect to Past –
Uniformitarianism
“The Present is the Key to the Past”
Ripple Marks, Bay Beach
Fossil Ripple Marks, Baraboo Range
Modern Mud Cracks
Fossil Mud Cracks, Virginia
Two Kinds of Ages
Relative - Knowing Order of Events
But Not Dates
 Civil War Happened Before W.W.II
 Bedrock in Wisconsin Formed Before The
Glaciers Came
Absolute - Know Dates
 Civil War 1861-1865
 World War II 1939-1945
 Glaciers Left Wisconsin About 11,000
Years Ago
Stratigraphy
Reading the rock layers
The principle of superposition.
In an uninterrupted sequence of sedimentary rocks, the
rock layers below are older than rock layers above.
The principle of superposition.
In an uninterrupted sequence of sedimentary rocks, the
rock layers below are older than rock layers above.
The principle of original horizontality.
Sediments that form sedimentary rock are laid down in a
horizontal position due to gravity.
The principle of original horizontality.
Sediments that form sedimentary rock are laid down in a
horizontal position due to gravity.
The principle of cross-cutting relationships.
Where one type of rock cuts across or through another,
the rock that has been cut is older and the rock which did
the cutting is younger.
The principle of cross-cutting relationships.
Where one type of rock cuts across or through another,
the rock that has been cut is older and the rock which did
the cutting is younger.
The principle of cross-cutting relationships.
Where one type of rock cuts across or through another,
the rock that has been cut is older and the rock which did
the cutting is younger.
Metamorphic
rocks:

A metamorphic rock is
always older than the nonmetamorphosed rocks
around it. The
metamorphic rock must
have formed before the
surrounding rocks,
otherwise they would be
metamorphosed as well.
The principle of inclusions.
If a rock contains pieces of a different rock, the pieces
must be from an older rock.
The principle of inclusions.
If a rock contains pieces of a different rock, the pieces
must be from an older rock.
The principle of fossil succession.
Fossils – remains of organisms – occur in a determinable
order, and any given time period can be recognized by the
fossils present in rocks formed during that time.
The principle of fossil succession.
Fossils – remains of organisms – occur in a determinable
order, and any given time period can be recognized by the
fossils present in rocks formed during that time.
The principle of fossil succession.
Fossils found in rock are sequenced from simpler forms to
more complex form.
The principle of fossil succession.
Fossils found in rock are sequenced from simpler forms to
more complex form.
The principle of fossil succession.
Fossils found in rock are sequenced from simpler forms to
more complex form.
Rock strata and unconformities.
You
will notice that the top boundary of some of the rock layers is jagged.
This boundary, an unconformity, is where the rock layer’s surface was
exposed to wind and water erosion for a significant amount of time before
the next sediments covered it.
Put the Letters A-F in order, from oldest to youngest.
Explanations:
A - folded rock strata cut by a thrust fault;
B - large intrusion (cutting through A)
C - erosional unconformity (cutting off A & B) on which rock
strata were deposited
D - volcanic dike (cutting through A, B & C)
E - even younger rock strata (overlying C & D);
F - normal fault (cutting through A, B, C & E).
Breaks in the geologic record.
Angular unconformity.
Rock layers are tilted at an angle by uplift, faulting, or
folding; these layers are eroded and new horizontal layers
are created above them.
Breaks in the geologic record.
Disconformity.
Upper material is eroded and new material is deposited,
covering older rock. The most difficult to recognize.
Breaks in the geologic record.
Nonconformity.
Occurs with a metamorphic or intrusive igneous rock and
layers of sedimentary rock created above it. Created by
uplift and erosion with deposition on top of older rock.