Chapter 1

Plate Tectonics

1.1 Earth’s Interior

The Science of Geology

• Geologists: scientists who study the processes that create the Earth’s features and search for clues about Earth’s history

• Geology: the study of the planet Earth

• Continents: 7 great landmasses; North America, South America, Europe, Africa, Asia, Australia, Antarctica

The Science of Geology• Constructive Forces: Forces that shape

the Earth’s surface by building up mountains and landmasses. – volcanoes

• Destructive Forces: forces that breakdown and wear away mountains and other features on the Earth’s surface– Water! wind, waves, ice, hot and cold

The Science of Geology• Geologists study the way seismic waves,

the energy created by earthquakes, travel through the Earth in order to infer what the inside of the Earth is like

• The Earth is made up of 3 main layers: the crust, mantle, and the core

• Both temperature & pressure increase as you move in towards the center of the Earth

Earth’s Structure

The Crust

• Crust: the layer of rock that forms the Earth’s outer skin– It is the thinnest beneath the oceans and

thickest below mountains

• Oceanic crust: made of a dark, dense, fine textured rock called basalt

• Continental Crust: made of light colored, coarse textured, less dense rock called granite

The Mantle

• Mantle: solid layer of hot rock that behaves plastically– The uppermost portion of the mantle and

crust make up the lithosphere: the rigid outer layer

– The lithosphere floats on the asthenosphere: the softened rock between the lithosphere and core that behaves plastically

The Core

• Core: the center of the Earth composed of 2 layers made of the dense metals iron and nickel– Outer core: liquid molten metal– Inner core: dense ball of solid metal

Density

• Density is a measurement of the amount of matter packed into a certain volume of a substance.

• Density = Mass

Volume

• Brainpop

1.2 Convection Currents and the Mantle

Heat Transfer

• Heat transfer: the movement of energy from a warmer object to a cooler object

• 3 types

1. Conduction

2. Convection

3. Radiation

Conduction

• transfer of heat through direct contact of particles (solids!)

Convection• the transfer of heat

through liquids and gases

• Caused by differences between temperature and density in a fluid

Radiation

• The transfer of energy through empty space

• Ex. The sun warming the earth’s surface

• No direct contact between heat source and object

Density

• Density: Measure of mass in a volume of a substance (Density = Mass / Volume )– When a liquid or gas is heated the particles

speed up and spread out (volume increases) as a result density decreases

Convection current

• Convection Current: The movement of a fluid or gas, caused by differences in temperature and density, that transfers heat from one part of the fluid or gas to another– With out heat convection stops– Within the Earth heat from the core cause

convection currents to form in the asthenosphere

1.3 Theory of Continental Drift

Alfred Wegener• German scientist

who first proposed continental drift

• His hypothesis: that all the continents were once joined together and have since drifted apart

Pangaea

• Supercontinent that existed 300 MYA (million years ago) means “all lands” in Greek

Continental Drift

• Idea that the continents moved slowly over the Earth’s surface

Wegener’s Evidence

1. Landforms: mountains in Africa line up with mtns in S. America & coal fields in Europe match ones found in N. America

2. Fossils: The same fossils are found in Africa, S. America, Australia, India, and Antarctica **Glossopteris – fern**

3. Climate: Tropical plant fossils found in Norway indicate it used to be warm & evidence of glaciers in Africa indicate it used to be cold Therefore the continents MUST have moved

Fossil Evidence

Landform Evidence*mountains*

Landform & Climate

Evidence

*glacial grooves*

Climate Evidence Glossopteris (ferns) in Africa

Wegener’s Rejection

• Scientists rejected Wegener’s theory because he could not prove “how” or “why” the continents moved

• This continued until the 1960’s!!!!

Plate Tectonics Brain Pop

1.4 Sea Floor Spreading

Mid-Ocean Ridge• Undersea mtn. chain where new ocean floor is produced

(divergent boundary); discovered in mid 1900s using sonar

• Mid-Atlantic Ridge longest mtn chain in the world!

Harry Hess

• American geologist that suggested that the oceans move like conveyer belts carrying the continents with them

Sea-floor spreading

• Movement begins at mid ocean ridge, where molten material rises from the mantle and erupts

• The molten material spreads out pushing older rock outward

Interactive Picture

Sea-Floor spreading• The process described above that continually

adds new material to the ocean floor.

Divergent Boundary

Evidence

1. Molten Material - Pillow lava is formed when magma erupts under water

2. Magnetic Stripes - Magnetic stripes in the rock of the ocean show the direction of the Earth’s magnetic field at the time the rock hardened (pole reversals). The pattern is the same on both sides of the ridge.

3. Age of Rocks - The further away from the mid-ocean ridge the older the rocks are

Pillow Lava

Magnetic Stripes

Age of Rocks

Age of oceanic crust: youngest = red; oldest = blue

Subduction at Deep Ocean Trenches

• At deep ocean trenches subduction allows part of the ocean floor to sink back into the mantle– Deep ocean trench: Underwater canyon

where ocean crust sinks back into the mantle– Subduction: Process by which ocean floor

sinks beneath a deep ocean trench and back into the mantle

Subduction at Deep Ocean Trenches

1. In the Pacific -There are many trenches; it is shrinking!

2. In the Atlantic - Few trenches; it is expanding!

Ocean Floor Brain Pop

1.5 The Theory of Plate Tectonics

Theory of Plate Tectonics • States that pieces of the Earth’s

lithosphere are in constant, slow motion, driven by convection currents in the mantle

– It explains the formation, movement, and subduction of the Earth’s plates

• Plates: Pieces of the lithosphere broken into separate sections floating on the asthenosphere

Plate Boundaries• 3 kinds of plate boundaries

1) Divergent – The place where 2 plates move apart, or diverge

2) Convergent – The place where 2 plates come together, or converge, resulting in a collision

3) Transform – A place where 2 plates slip past each other moving in opposite directions; Ex. San Andreas fault

Transform Boundary

• A break in the Earth’s crust where slabs of rock slip past each other

Divergent Boundaries

1. Mid-ocean ridge: where plates are spreading apart in the middle of the ocean

Mid-Atlantic Ridge: Longest mountain chain in the world!!!

2. Rift valley: where a continental plate is pulling apart (Great Rift Valley in Africa) and a sea may eventually form

Mid-ocean Ridge

Interactive Picture

Rift Valley

Rift Valley

Ex. The Red Sea

Convergent Plate Boundaries1) Ocean-Ocean: Island arc forms where the

denser of 2 oceanic plates subducts below the other (Indonesian Islands / Aleutian Islands)

2) Ocean-Continent: Where denser ocean crust subducts (into a trench) below the lighter continental crust; volcanic coastal mtn. ranges often result (Cascades / Andes)

3) Continent-Continent: 2 continental plates collide and no subduction occurs; tall mtn. ranges are created (Himalayas) folded mtns

Convergent Plate BoundariesOcean - Continent

Convergent Plate BoundariesOcean - Ocean

Convergent Plate Boundaries

Continent - Continent• Himalayan

Mountains

Convergent Plate Boundaries

Folded Mountains

Continent - Continent