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

3. Igneous Intrusion Younger than surrounding rock, look for contact metamorphism in layer above and below the intrusion

Which letter represents the intrusion?

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 represents the extrusion? D

5. Faults, folds, tilting of rock layers - UPLIFT

Fault Cracks in rock layers, layers are ________ (rock layers are no longer even) off-set

Folds Bends in rock layers due to plates converging.

Tilting of rock layers Rock layers are now at an angle

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 B C D E F G X H I J K L Y Relative Age: List the following rock layer in chronological order starting with the oldest layer.