Download Earth`s Structure

Chapter 8
The Dynamic Planet
The Dynamic Planet
 Geologic time scale
 Earth’s structure
 Geologic cycle
 Plate tectonics
Big ideas
 Catastrophism = young, fast Earth
 Uniformitarianism = old, slow Earth
Geologic Time Scale
 Age of Earth 4.6 by
 Oldest rock 3.96 by
 Life 3.4 by
 K-T boundary 66.4 my = end of dinosaurs
 Pleistocene 1.6 my
 Holocene 10,000
Cosmic Year
 Earth formed January 1st
 Oldest rock Valentine’s Day February 14th
 Life! March 1st
Cretaceous-Tertiary end of dinos evening of December 25th
 Humans December 31st 11:49:35

Earth’s Structure
 Layers of material sorted by density
 Core
 Mantle
 Lithosphere
Earth’s Structure
 Core
Inner core solid iron 13.5 g/cc
 Outer core liquid iron 10.7g/cc
 Mantle
 Lower mantle solid
 Upper mantle solid
 Asthenosphere caramel layer

Earth’s Structure
 Lithosphere
Uppermost mantle solid (confusing no?)
 Crust = foamy, scum that floated to top
Oceanic crust 3g/cc
Continental crust 2.7g/cc

Earth’s magnetic field
 Created by spinning outer core
 Reverses aperiodically
 9 reversals in last 4 million years
 Some last millions of years, some thousands
 Reverses full strength then decays to nothing for a few
thousand years
Isostacy
 Crust floats
 Higher mountains have deeper roots
 Oceanic crust may be 5 km thick
 Continental crust 30-60 km thick
Rock cycle
 Sedimentary = made from sediment
 Igneous = once molten
 Metamorphic = heated or compressed or both
Igneous rock
 Intrusive cools within Earth
Slow cooling allows large crystals to form
 Granite’s crystals
 Extrusive cools at surface
 Quick cooling makes small crystals
 Obsidian = volcanic glass

Plate tectonics
 Proposed by many people
 Alfred Wegener proposed idea of continental drift in 1912
 Used geologic evidence, fossil evidence, continental margins
 1960s flood of data confirmed Wegener’s idea, now called plate
tectonics
Plate tectonics
 14’s major rigid plates moved by caramel like asthenosphere
 Major evidence (along with Wegener’s)
Magnetic reversals along spreading centers in mid-oceanic
ridge
 Spreading rates
 Ages of crust

Plate tectonics
 Oldest crust 208 my, found off Japan
 All continents together 225 mya, called Pangea
 All were together 465 mya?
Review Questions
 1, 2, 3, 5, 6, 7, 9, 10, 17, 19, 20, 21, 22, 23