Plate tectonics

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When and who first proposed the theory of continental drift?

Alfred Wegener in 1915

What book did Wegener publish?

The origins of continents and oceans

What was the continental drift hypothesis?

1. There used to be a super continent called Pangaea and it started breaking apart about 700 million years ago
2. The continents "drifted" to present positions
3. Continents "broke" through the earths crust

What evidence did Wegener use to support his hypothesis?

1. The continents fit together
2. Fossils match across the sea
3. Rock type and structures match
4. Ancient climates

Why is the continents fitting together one of Wegener's points?

They fit together so perfectly, it couldn't be a coincidence

What is a mesosaurus and where were its fossils found?

A sharp-toothed, freshwater reptile found in South America and Africa

What are cynognathus and lystrosuarus and where were their fossils found?

A mammal like reptile found throughout continents in the southern hemisphere, separate by ocean

What is a glossopteris and where were its fossils found?

A fern found in South America, Africa, Australia, India and Antartica

What did Wegener mean when he said "ancient climates"?

The presence of glaciers from before left rock markings when they retracted or advanced

What is paleoglaciation?

It refers both to the extent of ancient glaciers and to the rock markings they have left behind

Where was paleoglaciation found?

In parts of the world that are now tropical (Example: India, Africa)

What did Wegener notice about mountain ranges?

Some began on one continent, end at the coastline, and then appear to begin in another continent across the ocean

How did Wegener know these mountain ranges used to be connected?

There were similarities in rock structures and the age of rocks in mountain ranges that were across continents

Why did no one believe Wegener at first?

He couldn't prove why the continents drifted

What did scientists believe the earth was 4.5 billion years ago?

A molten ball of magma and fire

How did the molten ball of fire become our earth today?

As the earth cooled and denser materials sank toward the Earth's core, less dense materials floated to the top (this formed the earth's crust)

What are the five distinct layers of the earth?

Crust, mantle, outer core, inner core

What is the crust of the earth?

The outer solid rock layer

What is the mantle?

It is the thickest layer of the earth and there are two parts: Upper and lower

Upper is molten rock (a similar thickness to toothpaste)

Lower is solid rock

What is the outer core?

A layer of molten metal (iron and nickel)

What is the inner core?

A dense, solid ball of (mostly) iron. It is EXTREMELY hot and has LOTS of pressure

What are the two types of crust?

Continental and oceanic

Why does the crust float above the mantle?

The crust is less dense than the mantle

Which of the two crusts are denser?

The oceanic crust (this is why continental crusts are higher in elevation)

What did everyone believe in the mid 1900's?

The earth was flat, the ocean crust never changed and older than the continental crust

Why did everyones views change?

Because of world war 2, scientists were making new technology

What is a magnetometer?

An instrument that detects small changes in magnetic field

What is a sonar?

An instrument that uses sound waves to measure distance by measuring the time for sound waves to bounce off the seafloor and return to the ship

How did the sonar help us?

It helped to map the topography of the sea floor

What are mountain chains in the oceans called?

Ocean ridges

How long and tall is the longest ocean ridge on earth?

65,000 km long and 3 km high

What are common natural disasters along ocean ridges?

Earthquakes and volcanism

What are deep-sea trenches?

A narrow, elongated depression in the sea floor

What two things did the analysis of rocks and sediments lead to scientists discovering?

1. Rock ages across the ocean vary: Rocks near the ocean ridges were younger than the rocks near the deep-sea trenches/shore

2. The thickness of sediments increases with distance from the ocean ridge

What is seafloor spreading?

The theory that explains how new oceanic crust is formed at ocean ridges, slowly moved away from ocean ridges, and destroyed at deep-sea trenches

Draw a diagram of seafloor spreading

What are tectonic plates?

Huge pieces of crust and ridges upper mantle that fit together to cover the earth's surface

What is the plate tectonic plate theory?

Plate tectonics is the theory that describes how tectonic plates move and shape earths surface

Why do plates move?

Convection currents in the mantle

How fast do plates move?

It is different for every plate, but about the same speed as your nails grow

What are divergent plate boundaries?

When two plates move apart

How is new seafloor formed?

Mantle material upwells

Where do ocean ridges and seafloor spreading occur?

At divergent plate boundaries

When do rift valleys form?

When two plates diverge on a continent

Where are rift valleys usually located?

Along oceanic ridges

What are convergent plate boundaries?

When plates collide

What are the three types of plate boundaries?

1. Oceanic - continental convergence
2. Oceanic - oceanic convergence
3. Continental - continental convergence

What are oceanic - continental plate convergence?

When the oceanic slab sinks into the mantle

What is subduction?

The action of one tectonic plate pushing below another tectonic plate

How does subduction work?

Pockets of magma develop and rise

What does subduction form?

Continental volcanic arcs

What is an example of convergent plate boundaries?

The Andes mountains

What is oceanic - oceanic convergence?

When two oceanic plates converge and one descends beneath the other

What does oceanic - oceanic convergence form?

Volcanos on the ocean floor

How do volcanic island arcs form?

When volcanos emerge from the sea

What is an example of a volcanic island arc?

Japan or Hawaii

What is continental - continental convergence?

When two continents collide and uplift

What is important to remember about continental - continental convergence?

There is no subduction

What does continental - continental convergence cause?

The himalayan mountains

What are transform fault boundaries?

When plates slide past each other

What is important to remember about transform fault boundaries and crust?

1. No new crust is created
2. No crust is destroyed

What is an example of transform fault boundaries?

The San Andreas Fault

What type of plate boundaries cause earthquakes?

Transform bounderies

What is a super volcano?

A volcano that is MUCH larger than a normal volcano (it has a larger magma chamber)

What would happen if a super volcano exploded?

It would be catastrophic and kill millions or billions

Where is the closest super volcano to us right now?

In Yellowstone National Park

What is the closest volcano to us?

Mt. Baker and Mt. Saint Helens