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Lecture 23

Lecture 23 - Geologic Time Scale Boundary based Boundary on...

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Unformatted text preview: Geologic Time Scale Boundary based Boundary on mass extinction (dinos and others) Boundary based Boundary on major mass extinction called the Great Dying Great Boundary based Boundary on widespread appearance of hard-shelled organisms organisms Older subdivisions of Cenozoic of 09.08.a1 How Fossils Change in Sequence of Sedimentary Rocks Can use overlap of two fossils to constrain age Some spanned long times Some species lived short time Some span so give narrow age range span Fossils change up section Fossils in systematic way in 09.07.a1 These two sections of rock contain many of the same These fossils. Match the two sections, envisioning dashed lines connecting places where the two sections correlate (i.e., represent the same time). correlate 09.07.b1-2 Comparing Partly Overlapping Sections Observe how these rock sections correlate and how the thicknesses of some units vary 09.07.b3-4 Using both sections, we can reconstruct a more complete section Assigning Numeric Ages to Timescale Date a volcanic layer Date a dike or clasts 09.08.b Bracket fossilbearing bed by bearing dating volcanic units dating Using Timescale to Assign Numeric Ages Use fossils and timescale Use to assign numeric age to Bracket using fossil ages from timescale timescale 09.08.c Bracket age using fossil Bracket and numeric ages Evidence that Earth’s History is Not Short Tree rings 09.09.b Varves Current rates of Current plate motion plate Where Age of Earth Comes From Age of Age meteorites meteorites Dated Moon Dated rocks rocks Oldest dates on Oldest Earth rocks Earth 4.55 billion 4.5 billion 3.9 to 4.0 b.y. (rock) 3.9 to 4.3 b.y. (grains) to Data from astronomy on age of Data Solar System and Universe Solar 09.09.d Precambrian Life Stromatolites Bacteria Cambrian Explosion Trilobites Brachiopods 09.10.a Life in the Paleozoic Early Paleozoic Middle Paleozoic Late Paleozoic 09.10.c Life in the Mesozoic Early Mesozoic: Triassic Middle Mesozoic: Jurassic Late Mesozoic: Cretaceous 09.11.a Life in the Cenozoic Early Cenozoic Late Cenozoic 09.11.c Correlating Units and Events Observe these Observe two sections, noting how each layer correlates or doesn’t from one section to another another Can use: • Rock type Rock • Position in sequence Position • Fossils Fossils • Numeric ages Numeric • Magnetic sequence Magnetic 09.12.a1 Observe this perspective and consider how rock units Observe could change from one section of rocks to another could Facies change Sand Sand dunes dunes Eroded away Ocean Delta River River deposits deposits Restricted event or environment Change in thickness 09.12.b1 On this geologic On map, features are numbered in the order they occurred. Identify reasons why the units and features are interpreted to have formed in this relative order. order. 3 2 11 – Scoria 11 Cone Cone 09.12.c1 9? 7 – Sand 8 1 11 – Lava Flow Flow 7 – Sand t es h ig r H – aye 5L 4 t es w Lo yer – 2 La 10 – Fault 7 – Sa nd 3 1 – Granite 6 – ike D Observe each figure and Observe think about how the information is important in determining potential for geologic hazards for Lava flow Lava covering scarp covering 09.13.a Younger lava Younger flow flow Older Older lava flow lava Flo od pl a in Fresh scarp scarp Eroded Eroded scarp scarp High High terrace terrace High High terrace terrace Observe this satellite image of the Grand Canyon 09.14.a Geologic History of Grand Canyon, Part 1 09.14.a5 Geologic History of Grand Canyon, Part 2 09.14.a5 Observe this Observe stratigraphic section and match the units and unconformities with the sections in the photographs the Late Paleozoic Late Middle Middle Paleozoic Paleozoic Late Paleozoic Late Middle Middle Paleozoic Paleozoic Early Paleozoic Early Paleozoic Upper unconformity Late Precambrian Late Lower unconformity Precambrian basement Early Paleozoic Late Precambrian Late Precambrian Precambrian basement basement 09.14.a Investigation: What Is the Geologic History of This Place? Observe this area and Observe determine the ages of events. F A B C D F V L B F G C G 09.15.c1 A C D R R K S N A R L D G ...
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