Geologic History & Sequencing

Geologic history

The study & interpretation of Earth's past

Principle of uniformitarianism

 the geologic history processes that are going on now happened before.

• "The present is the key to the past"

• -Ex; Places today where layers of sediments are forming in a pattern, that same pattern can be found in rocks formed long ago

Relative age

When the age of a rock or event is compared to the ages of other rocks or events in geologic history, the relative of the rock or event is determined.

Absolute age

The actual age of the rock or event.

• The older it is the more hard it gets to determine the absolute age

Principle of original horizontality

sediments are deposited in horizontal layers that are parallel to the surface on which they were deposited.

• Tilted or folded layers indicate that the crust has been deformed.

Principle of Superposition

 In a series of undisturbed layers, the oldest is on the bottom. 

• The principle of superposition does not apply, however, in cases where layers have been overturned or where older rocks  have been forced over younger layers along a fault. 

Intrusions

When molten magma forces its way into cracks or crevices in crustal rock and solidifies it forms a mass of igneous rock.

Extrusion

When lava solidifies at Earth’s surface and it forms a mass of igneous rock.

Unconformities

Buried Surfaces that indicate gaps or breaks in the geologic time record.

• These gaps represent destruction of the geologic record.

Angular unconformities

 Tilted folded or faulted rocks which have been eroded and then covered again.

Parallel unconformities

also called disconformities, occur when parallel rock layers of different ages are separated by an erosional surface .

Nonconformities

Formed when sedimentary rocks are deposited on top of an eroded surface of igneous

The diagram below represents folded and faulted rock layers cut by an igneous intrusion. What is the relative age of the intrusion?

younger than rock unit D and younger than the fault

The sedimentary bedrock in both regions originally formed as…

horizontal layers

Which rock layer provides the best evidence for crustal movement?

Layer B

Which rock layer most likely was deposited directly on an erosional surface?

Layer C

Which event occurred most recently

erosion of rock layer J