Transcript File
Do First Actions: Turn in your Geological Time Scale Worksheet Write PSAT for the Do First and DYL yesterday. Do First: 1. A footprint is an example of what type of fossil? 2. What are the characteristics of an index fossil? Relative Dating What can rocks tell us? • Rocks hold a record of geological events and life form changes of the past • Uniformitarianism means that the forces and processes that we observe today have been at work for a very long time. – Examples: tides, gravity Relative Dating • Relative dating tells us the sequence in which events occurred, not how long ago they occurred. • Which example below is an example of relative dating? – This rock is 500 million years old and this rock is 3,000 years old – This rock formed first and then this rock formed next Rules of Relative Dating 1. 2. 3. 4. 5. 6. Principle of Superposition Principle of Original Horizontality Principle of Cross – Cutting Relationships Principle of Inclusions Uncomformities Principle of faunal succession Principle of Superposition • The principle of superposition states that in an undisturbed layer of rock, the oldest rocks are on the bottom and the rock layers become younger going up. Principle of Superposition • In the diagram below label the layers: oldest, 2nd oldest, 3rd oldest, youngest Ordering the Grand Canyon’s History Principle of Original Horizontality • The principle of original horizontality means that layers of sediment are generally deposited in a horizontal position. Principle of Original Horizontality • Label the younger and the older hill. Principle of Original Horizontality • Label the younger and the older hill. Changed over time Disturbed Rock Layers Principle of Cross-Cutting Relationships • The principle of cross-cutting relationships states that when a fault cuts through rock layers or when magma intrudes other rocks and crystallizes (dike) , we can assume that the fault or intrusion is younger than the rocks affected. Which occurred last? • For each picture below order the layers from youngest to oldest. Put a 1 next to the youngest layer and a 2 next to the next youngest and so forth. Principle of Inclusions • Inclusions are rocks contained within other rocks. • Rocks containing inclusions are younger than the inclusions they contain. Inclusions Unconformities • An unconformity represents a long period during which deposition stopped, erosion removed previously formed rocks, and then deposition resumed. – In easier terms, rocks settled, then got removed by wind or water and then new rock settled – Deposition is the settling of rock – Erosion is the movement of rock • An unconformity is essentially a missing layer of the rock record Types of Unconformities Types of Unconformities are: 1. Angular Unconformity 2. Nonconformity 3. Disconformity Angular Unconformity • An angular unconformity indicates that during the pause in deposition, a period of deformation (folding or tilting) and erosion occurred. Nonconformity • A nonconformity is when the erosional surface separates older metamorphic or intrusive igneous (non horizontal rock) rocks from younger sedimentary rocks (horizontal rock). Disconformity • A disconformity is when two sedimentary (horizontal) rock layers are separated by an erosional surface. Types of Unconformities Angular unconformity Disconformity Nonconformity A Record of Uplift, Erosion, and Deposition Principle of faunal succession • Principle of faunal succession states groups of fossil plants and animals occur in the geologic record in a definite and determinable order. • A period of geologic time can be recognized by its respective fossils. Principle of faunal succession • Attempt to put the following rock layers in order from youngest to oldest Practice On your DYL write: Exit Ticket