Earth ScienceCoach Williams

Room 310B

Plate Tectonics

Chapter 17

Objectives Describe one piece of early evidence that

led people to suggest the Earth’s continents my have once been joined.

Discuss evidence of continental drift Explain why continental drift was not

accepted when it was first proposed.

Section 17.1: Drifting Continents

Fit of continents across Atlantic Ocean Gondwanaland: southern continents

Early Observations

Gondwanaland

Theory that Earth’s continents were once joined.

Continents had slowly drifted apart Pangaea: “all the Earth”

Continental Drift

Rocks: similar rocks Fossils: animal/plant remains Ancient Climate: coal in Antarctica

Continental Drift Evidence

2 Reasons the theory was rejected◦ 1) What forces could cause them to move?◦ 2) How could continents move and not shatter?

Rejected Hypothesis

Objectives◦ Summarize the evidence that led to the

discovery of seafloor spreading.◦ Explain the significance of magnetic patterns on

the seafloor.◦ Explain the process of seafloor spreading.

Section 17.2: Seafloor Spreading

Sonar- sound waves to determine depth Magnetometer- detects changes in

magnetic fields Map the ocean floor

Help From Technology

Mountain ranges (ridges), trenches Earthquakes & volcanoes

Ocean Floor Topography

Ocean Floor Topography

Varying ages of rocks: pattern◦ Younger rocks near ridges◦ Older rocks farther away

Sediments◦ Thinner than continental crust◦ Thickness increased farther away from ridge

Ocean Rocks and Sediments

Paleomagnetism: study of magnetic record◦ Basalt(Iron) = compass needle

Magnetic reversal: change in Earth’s magnetic field

Magnetic symmetry: matching strips on each side of ridge

Magnetism

New crust created at ridges Crust is destroyed at trenches Magma comes out of ridges New rock pushes crust outward Provided evidence for continental drift

Seafloor Spreading

Seafloor Spreading

Seafloor Spreading

Seafloor Spreading

Objectives: Explain the theory of plate tectonics Compare/contrast the three types of plate

boundaries and the features associated with each.

Section 17.3: Theory of Plate Tectonics

Earth’s crust: large slabs called plates Major and smaller plates

Theory of Plate Tectonics

Earth’s Plates

Plate boundaries: where plates meet◦ Divergent◦ Convergent◦ Transform

Plate Boundaries

Plate Boundaries

Plate Boundaries

Plates moving apart Most on ocean ridges Rift valley: narrow valley along divergent

boundary

Divergent Plate Boundaries

Plates moving together◦ Oceanic crust – oceanic crust: volcanoes◦ Oceanic crust – continental crust: volcanoes◦ Continental crust – continental crust: mountains

Subduction- one plate goes below the other

Convergent Plate Boundaries

Convergent Plate Boundary

Plates slide horizontally

Transform Plate Boundaries

Objectives: Explain the process of convection Summarize how convection in the mantle

is related to the movements of tectonic plates

Compare/contrast the processes of ridge push and slab pull

Section 17.4: Cause of Plate Motions

Convection: movement due to temperature differences

Mantle has convection currents Currents move plates Ridge push- weight of ridge pushes plate

down Slab pull- weight of plate pulls plate down

Mantle Convection

Push and Pull