GLY 101 1st Edition Lecture 12Outline of Last Lecture I. Metamorphic EnvironmentII. Metamorphic FaciesOutline of Current LectureIII. Numerical and Relative DatesA. Basic Principles of Relative DatingIV. Inclusions and UnconformitiesCurrent LectureIII. Numerical and Relative Dating- numerical dates specify the actual number of years that have passedsince an event occurred. - radioactivity allows us to accurately determine numerical dates for rocks that represent important dates in Earth’s history.* before radioactivity geologists had to rely solely on relative dating- relative dating is placing rocks in their proper sequence of formation. For example: first, second, third-relative dates cannot tell how long ago an event took place, but it does tell that one event followed another.A. The basic principles of relative dating:1. principle of superposition2. principle of original horizontality3. principle of lateral continuityThese 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.4. principle of cross-cutting relationships1. Principle of superposition- Nicolas Steno is credited with being the first to recognize a sequence of historical events in sedimentary rock layers. - law states that in an undeformed sequence of sedimentary rock, each bed is younger than the one below and older than the one above it.-in 1669, Steno stated this principle.2. Principle of Original Horizontality-Steno is also credited with recognizing the importance of the principle of original horizontality.- this law says that layers of sediment are generally deposited ina horizontal position. -rock layers that are flat have not been disturbed and still have their original horizontality; however, if they are folded or inclined at a steepangle , they must have been moved by after deposition.3. Principle of Lateral Continuity- sedimentary beds originate as continuous layers that extend in all directions until they eventually grade into a different type of sediment oruntil they thin out at the edge of the basin of deposition.IV. Inclusions and Unconformities - inclusions are fragments of one rock unit that have been enclosed within another.- the rock that contains the inclusion is the youngest.- rock layers that have been deposited without interruption are conformable.- unconformities represent long period during which deposition ceased, erosion removed previously formed rocks, and then deposition resumed.- unconformities represent significant geologic events.- three types of unconformities:1. angular conformity- most easily recognized unconformity.- consists of tilted or folded sedimentary rocks that overlain by younger, flat lying strata.-indicates that during the pause in deposition, a period of deformation and erosion occurred.2. disconformity- a gap in the rock record that represents a period during which erosion instead of deposition occurs.3. nonconformity-when younger sedimentary strata overlie older metamorphic or intrusive igneous rocks.- in order for a nonconformity to develop, there must be a period of uplift and erosion of overlying