Download Rock Cycle Earth`s History In Rock Layers Evidence of Earth`s

Rock Cycle
Laws when “dating” rock layers:
These laws are based on the assumption that the forces at work today are the same
forces at work throughout Earth’s History: UNIFORMITARIANISM
Law of
In horizontal sedimentary rock layers, the oldest layer is on the
Superposition
bottom and each higher layer is younger than the layer underneath
Law of Original
Horizontality
Law of
Cross-Cutting
Relationships
All rocks are initially deposited in flat
(horizontal) layers
Objects which cross cut rocks are
younger than the rocks themselves
(ex: fault or intrusion)
Forces disturb rock layers: erosion, plate movement, volcanic
Unconformity
A gap in the geologic record where some rock
layers have been lost due of weathering and
erosion. (wind, water, ice wedging)
Fault
Earth’s History In Rock Layers
Evidence of Earth’s history is found in rock layers. How they are arranged, what is in those
layers and any disturbances in those layers tell a story. There are three important tools we
use in determining the age and order of events in rock layers:
Relative Age
Rock’s age when compared to the ages of other rocks. Layers of
rock that are younger will be deposited on top of layers of rocks
that are older.
Fossils are the same age as the rock layer in which they are found
Index Fossils
A fossil that
- widely distributed geographically (large horizontal distribution)
- lived for a short period of time (small vertical distribution)
Absolute Age
Using the half-life of a radioactive material deposited in rock layers
to determine the “exact” age of the rock.
Intrusion
Overturning
A break in earth’s crust. The fault will have
occurred after the layers it cuts across and
before the horizontal layers above it.
Lava cuts/melts through rock layers in
Earth’s crust. It cools and hardens into
igneous rock.
Horizontal rock layers tilt or fold due
to movement of tectonic plates.