Warm-up #43 Mar. 26

Brainstorming:Will California eventually slide into the ocean?

Have continents really drifted apart over the centuries?

PLATE TECTONICS

Unit 8

Continental Drift

Alfred Wegener – German scientist proposed the theory of continental drift.

This hypothesis stated that the continents had once been joined to form a single supercontinent

Pangaea – all land

Pangaea

Part of Wegener’s theory was that Pangaea started splitting into smaller continents 200 million years before

Wegener collected lots of evidence to prove this theory

The Continental Puzzle

The shorelines of the continents nearly fit together to make a large land mass.

HOWEVER The shorelines are constantly eroding and

changing.

Matching Fossils

Fossil evidence for continental drift includes several fossil organisms found on different landmasses.

At one point the theory was that there were land bridges, however there is no evidence of this.

Rock Types and Structures Several mountain belts that end at one

coastline reappear on a landmass across the ocean

Ancient Climates

Wegener found glacial deposits showing that between 220 million and 300 million years ago ice sheets covered large areas of the S. Hemisphere

Rejecting Wegener’s Hypothesis

Many scientists questioned Wegener’s theory

He could not describe a mechanism that was capable of moving the continents

There was not enough evidence

A New Theory

In 1968 a new theory was proposed –

PLATE TECTONICS

Plates

The lithosphere is broken up into segments called plates

The lithosphere is the uppermost layer of the mantle

Plates continuously move and change shape and size

Warm-up #44 Mar. 27 Mesosaurus provided evidence that South

America and Africa were once joined

On average, how much do you think the plates move a year?

5 centimeters

Plate Boundaries

A plate boundary is where two plates meet.

There are three main types of boundaries:DivergentConvergentTransform fault

Divergent

Also called spreading boundaries Occurs when two plates move apart Results in upwelling of material from the

mantle to create new seafloor

Convergent

Form where two plates move together Results in lithosphere plunging beneath

an overriding plate and descending into the mantle

Transform fault

Margins where two plates grind past each other without the production or destruction of lithosphere

What happens at boundaries?

Divergent BoundariesSeafloor spreading occurs along the

boundaryForms fractures on the ridge crestsFractures fill with molten materialWhen the boundary occurs on a continent,

rifts or rift valleys form

Convergent Boundaries

Oceanic-continental boundaryForms a subduction zone withinVolcanic arcs form

Oceanic-oceanic boundaryOften forms volcanoes on the ocean floorIsland arc forms as volcanoes emerge

Convergent Boundaries

Continental-continental boundariesNeither plate will subductCan produce mountains

Transform Fault Boundaries No new crust created No crust is destroyed Most are in oceanic crust Parallel the direction of

plate movement Aids movement of crustal

material

Boundary Brochures Needs to include:

3 types: Divergent, Convergent, TransformWhat each one is (use your notes)A picture for eachAn example for each

○ http://geology.com/plate-tectonics.shtmlNeeds to be colored

Warm-up #45 Mar.28Brainstorming: Do you think it is possible for Earth’s

magnetic poles to be reversed? If so, what do you think could happen to

the biosphere? Also, how might geologist use that to

support plate tectonics?

Evidence for Plate Tectonics Paleomagnetism

Most persuasive piece of evidence.Ancient magnetism preserved rocks.Paleomagnetic records show:

○ Polar wandering○ Earth’s magnetic field reversals

Evidence for Plate Tectonics Earthquake patterns

Associated with plate boundariesDeep-focus earthquakes along trenches

provide a method for tracking the plate’s descent

Evidence for Plate Tectonics Ocean Drilling

Deep Sea Drilling Project – Glomar Challenger

Age of deepest sediment○ Youngest are near the ridges○ Older are at a distance from the ridge

Ocean basins are geologically young

Evidence for Plate Tectonics Hot Spots

Rising plumes of mantle material.Volcanoes can form over

Driving Mechanism

No one model explains all plate motion Earth’s heat is the driving force Several models have been proposed

Convection currents in the mantleSlab-pull and slab-push model Hot plumes

Dynamic Earth http://www.learner.org/

interactives/dynamicearth/index.html

Ticket out the Door

1. What are the 3 main types of plate boundaries?

2. Name 2 pieces of evidence Wegener used to prove continental drift.

3. What is type of boundary is this?