Midterm 4 Chaper Outlines 8,12,15,21

Midterm 4 Chaper - Geology 101 Midterm 4 Chapters 8 12 15 21 Chapter 8 Clocks in Rocks Relative Age-determining when something formed or happened

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Geology 101: Midterm 4 Chapters 8, 12, 15, 21 Chapter 8: Clocks in Rocks Relative Age-determining when something formed or happened in relation to other things Absolute/Radiometric age-determining when something formed or happened in units of time (e.g. days, years, Ma, etc.) Ma vs. Mya Ma when something formed (ex. 1988) never changes Mya how long ago something formed (ex. 19 years ago) changes relative to when you refer to it Stratigraphy-the study of strata (layers) in rocks Stratigraphic succession-a chronologically ordered set of strata Principles of Stratigraphy Original horizontality - sediments and most lava flows are deposited under the influence of gravity as nearly horizontal beds (lava sheets) Superposition - each sedimentary layer of an undisturbed sequence is younger than the one beneath it and older than the one above it Faunal succession - sedimentary rocks in an outcrop contain fossils in a definite sequence
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Layers with the same fossils are the same age Law of Inclusions Any piece of rock that has become “included” in another rock or body of sediment must be older than the rock or sediment into which is has been incorporated Unconformity a gap in the rock record where geologic time (and therefore rocks) are missing formed wherever layers were not deposited or were removed by erosion o disconformity - An unconformity between parallel strata or lava flows o angular unconformity - An unconformity between two sets of strata that are not parallel o nonconformity - unconformity between younger sedimentary rocks and adjacent, eroded metamorphic or igneous rocks. NOT AN INTRUSION! Cross-cutting relationships Any feature that cuts across a rock or body of sediment must be younger than the rock of sediment that it cuts across o features includes faults, intrusions, joints, etc Geologic Time Scales: Relative Ages Divisions of Geologic Time o Marked by specific set of fossils, boundaries of time indicate abrupt changes in fossils Eon Era Period Epoch (Longest shortest) Eras are basic time scales of Relative aging: Paleozoic, Mesozoic, Cenozoic (today) End of Mesozoic Dinosaurs died, beg. Cenozoic
Background image of page 2
End of Paleozoic Largest extinction ever, beg. Mesozoic Periods Named for geographic locality where formations are first/best described, or distinguishing characteristic of formations. Today we are in Neogene period Epoch Today we are in Holocene Epoch Major boundaries correspond with mass extinctions Minor boundaries correspond with relatively minor extinctions Relative ages can only tell us the order of geologic events through time. Measuring
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/30/2008 for the course GEOL 101 taught by Professor Mapes during the Fall '07 term at UNC.

Page1 / 23

Midterm 4 Chaper - Geology 101 Midterm 4 Chapters 8 12 15 21 Chapter 8 Clocks in Rocks Relative Age-determining when something formed or happened

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online