Transcript EARTH`S HISTORY

GEOLOGIC HISTORY
UNIFORMITARIANISM
“THE PRESENT IS THE KEY TO
THE PAST”
What is happening today geologically must
have happened in the past.
Ex. Weathering and Erosion, Plate
Tectonics, etc
Relative Age vs. Absolute Age
• Relative - Age of rock or event is
compared to ages of other rocks or events
in a geologic sequence
• Absolute Age – Actual Age
RELATIVE AGE
• (Determining Sequence of Events)
Law of Original Horizontality
1.Sediments are
deposited in
horizontal layers
2. Law of Superposition
Youngest layer
is on top, oldest
is on bottom
YOUNGEST
OLDEST
3. Igneous Intrusion
Younger than surrounding rock, look for
contact metamorphism in layer above and
below the intrusion
Which letter/layer
represents the intrusion?
H
4. Igneous Extrusion
-
rocks that formed from lava that reached
the surface of the earth
-
Younger than the rock layers below and
Older than any rock layer above it
-
Look for contact metamorphism on the
bottom only
Which letter/layer
represents the extrusion?
D
5. Faults and folds
Faults – cracks in rock layers, layers are
offset (rock layers are no longer even)
Folds – bends in the rock layers
Occur after the rock layers formed or
younger than rocks they are found in
6. Fossils
Are same age as
rock they are
found in the
living organism
lived during the
time the
rock layer was
forming
7. Unconformity
• Buried erosional surface
• >> uplift, erosion, subsidence, deposition
• Time gap in the rock record
• Indicated by a wavy line on diagrams
UNCONFORMITY
• Draw an arrow to the unconformity
UNCONFORMITY
• Subsidence – opposite of uplift, sinking of
land usually caused by erosion
• Isostatic balance – crust on
asthenosphere  if pushed up
somewhere it will sink somewhere else
Sequence the Event
1. Limestone
2. Sandstone (D)
3. Igneous Extrusion (C)
4. Shale (B)
5. Sandstone (A)
Sequence the Events
A
Relative Age: List the following rock layer in
chronological order starting with the oldest layer. B
C
D
E
F
G
X
H
I
J
K
L
Y