GEOLOGY 101 1st Edition Lecture 16 Outline of Last Lecture I. Types of MetamorphismII. Geological Time [Intro]Outline of Current Lecture I. Principles of Relative Datinga. Absolute DatingCurrent LectureStratigraphy: the description, correlation, and classification of strata in sedimentary rocks.Formation: a series of rock layers in a region that has similar physical properties, may contain the same fossils and is mapped as a unit.Principles of Relative Dating:1. Principal of original horizontality:- Sediments are deposited in horizontal beds.- If rocks do not lie in horizontal beds, they have been disturbed by some kind of tectonic force.- Exception: Crossbeds (deposited at an angle, not horizontal)2. Principal of Superposition:- In an undisturbed sequence of rocks, each layer is younger than the one beneath it and older than the one above it.3. Faunal Succession:- Fossils as timepieces - Use of index fossils to correlate rocks (formations) from different locations.4. Unconformities: - Markers of missing time- (deposition of rocks isn’t continuous forever)a) Disconformity: an unconformity in which the rocks above and below the unconformity are parallel.b) Angular Unconformity: not parallel due to folding and uplifting, erosion then takes part of the rock away, and new layers form on top of the unconformity.c) Nonconformity: sedimentary rocks in contact with crystalline igneous or metamorphic rocks. (dissimilar rock types in contact with each other)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.5. Cross-Cutting Relations:- Dike cross-cuts the pre-existing rock layers. Therefore, it is younger than the rock layers it cuts across.- Fault cross-cuts all rock layers. Therefore, the fault is younger than the rock layers it cuts across.Absolute Dating:- Absolute dating provides ages in years.- Radiometric Dating: uses unstable radioactive isotopes to determine absolute age.- The radioactive isotope, the parent isotope, evolves into a decay product, the daughter isotope, at a certain rate.o Isotopes: Atoms with identical # of protons, but different # of neutrons.o Radiometric Dating  the ratio of parent : daughter. Half-life: the time it takes for half of the parent to decay into daughterproduct.- Not all radioactive elements decay at the same rate, each isotope has a different