Chapter 8 The Dynamic Planet

Elemental Geosystems 5e

Robert W. ChristophersonCharles E. Thomsen

The Dynamic Planet

The Pace of Change

Earth’s Structure and Internal Energy

The Geologic Cycle

Plate Tectonics

The Pace of Change Geologic Time Scale

Uniformitarianism

Big ideasCatastrophism = young, fast Earth

Uniformitarianism = old, slow Earth

The present is the key to the past

Geologic Time ScaleAge of Earth 4.6 by

Oldest rock 4.25 by

Life 3.4 by

K-T boundary 66.4 my = end of dinosaurs

Cretaceous – Tertiary = K-T

Pleistocene 1.6 my

Holocene 10,000

Cosmic YearEarth 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

Geologic Time Scale

Figure 8.1

Geologic Time Scale

Figure 8.1

Earth’s StructureLayers of material sorted by density

Core

Mantle

Lithosphere

Crust

Earth in Cross Section

Figure 8.2

Earth’s Interior

Figure 8.2

Earth’s Interior

Figure 8.2

Figure 8.2

Earth’s Interior

Core to Crust

Figure 8.3

Earth’s magnetic fieldCreated 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

Magnetic Reversals

Figure 8.14

IsostacyCrust floats

Higher mountains have deeper roots

Oceanic crust may be 5 km thick

Continental crust 30-60 km thick

Isostatic Adjustment

Figure 8.4

The Geologic CycleThe Rock Cycle

Igneous processes

Sedimentary processes

Metamorphic processes

The Geologic Cycle

Figure 8.5

The Rock Cycle

Figure 8.6

Igneous Rock Types

Figure 8.7

Intrusive and Extrusive Rocks

Figure 8.8

Sedimentary Rock Types

Figure 8.9

Metamorphic Rocks

Figure 8.12

Plate Tectonics A Brief History Sea-Floor Spreading and Production of New Crust Subduction of the Crust The Formation and Breakup of Pangaea Plate Boundaries Earthquake and Volcanic Activity Hot Spots

Plate tectonicsProposed by many peopleAlfred Lothar Wegener proposed idea of continental drift in 1912Used geologic evidence, fossil evidence, continental margins1960s flood of data confirmed Wegener’s idea, now called plate tectonics

Plate tectonics14 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 tectonicsOldest crust 208 my, found off Japan

All continents together 225 mya, called Pangea

All were together 465 mya

Crustal Movements

Figure 8.13

Transform Faults, Plate Margins

Motion at Plate Boundaries

Continents Adrift

Figure 8.15

Continents Adrift

Figure 8.15

Continents Adrift

Figure 8.15

Plate Motions Through Time

Pangaea Breakup, Plate Movements

India Collision with Asia

Pangaea Breakup, Plate Movements

Plate Boundary Features

Earth’s Major Plates

Figure 8.16

Ocean Floor

Figure 8.17

Earthquakes and Volcanoes

Figure 8.18

Hot Spot Tracks

Figure 8.19

Hot Spot Volcano Tracks

Seafloor Spreading and Plate Boundaries

Transform Faults

Forming a Divergent Boundary

End of Chapter 8

Elemental Geosystems 5e

Robert W. ChristophersonCharles E. Thomsen