Age of Dinosaurs Lab 1: Geological Methods

Age of DinosaursGeological Methods

Who am I?

•Jeff Matzke

•Email: jeffrey-matzke@uiowa.edu

•Phone: (920)227-3779

•Office: 15H Trowbridge Hall

Office Hours

•15H Trowbridge Hall

•Monday 4:30 - 5:30

•Wednesday 10:30 - 11:30

•Friday 12:30 - 1:30

•If none of these times work for you feel free to email me to set up an appointment

Types of Rocks

•Igneous

•Metamorphic

•Sedimentary

Igneous Rocks•Formed by the cooling of magma or

lava

•Two types

•Intrusive or Plutonic

•Extrusive of Volcanic

Metamorphic•Formed by exposing any other rock

type to enough heat and pressure to be able to rearrange the molecules in the rock

Sedimentary•Formed when the weathered sediment

from any other type of rock settles and is cemented together

•Fossils are usually only found in in these

Types of Sedimentary Rocks•Clastic

•formed from weathered rock material (mudstone, siltstone, sandstone, ect.)

•Non-clastic

•usually formed through animal or plant processes (limestone and coal)

Dating Rocks

•Relative Dating

•Dating rocks in relation to each other (this rock layer is older than that rock layer)

•Absolute Dating

•Giving a date for when the rock layer was laid down (this rock layer is 3.15 million years old)

Superposition•Rock layers become younger

towards the top of a series of layers

Original Horizontality•It is always assumed that a rock

layer is put down horizontally and any deviation from the horizontal happened after deposition

Lateral Continuity•If the same apparent rock layer is

found across a valley, it is assumed to be the same rock layer unless there is evidence to the contrary

Cross-cutting Relationships•If a rock layer is disrupted by

cracks and other types or rocks are found in those cracks, the rocks found in the cracks are older than the rocks that are cracked

Faunal Succession•Sedimentary rocks that have the

same biological communities found within them are of the same age

Absolute Dating•Some elements are unstable and

decay into other elements (Uranium-238 decays into Lead-206)

•The amount of time it takes for one half of a sample to decay into the daughter material is called a Half-Life

Radiometric Dating•It is only possible to radiometrically

date igneous rocks

•So if you want to date a fossil you will have to find it between to igneous rock layers and then use relative dating methods

Radiometric Dating (example)

•Potassium-40 decays into Argon-40 with a half life of 1.248 billion years. You find a layer of igneous rock that has 75% of the original Potassium-40 and 25% Argon-40. How old is this rock layer?

(cont.)

•624 million years

Geological Time

•The Earth is really old (4.6 billion years)

•We break that time up into the Geological Time Scale

Units of Geological Time

•Hierarchical System (like biological classification

•Units

•Eon

•Era

•Period

•Epoch

Phanerozoic Eon•The last 540 million years

•Name means ‘visible life’

•Broken up into the Paleozoic Era, the Mesozoic Era, and the Cenozoic Era

Mesozoic Era

•The Age of the Dinosaurs

•Begins with the Permian-Triassic Extinction event 251 million years ago

Mesozoic Era (cont.)

•Triassic Period: 250-200 million years ago

•Jurassic Period: 200-145 million years ago

•Cretaceous Period: 145-65 million years ago

Stuff to take away

•There are three types of rocks; igneous, metamorphic, and sedimentary

•Fossils form in sedimentary rocks

•There are two ways to date rocks; relative and absolute dating

Stuff to take away (cont.)

•By using superposition, faunal correlation, and radiometric dating we can put geological events in sequence

•The Phanerozoic Eon is broken up into the Paleozoic Era, the Mesozoic Era, and the Cenozoic Era

•The Mesozoic is broken up into the Triassic, Jurassic, and Cretaceous (know the dates for the beginning and end of these periods)