The Earth &Plate Tectonics

Earth’s Layers(Solid)

(Liquid)

(Viscous)

(Rocky)

The crust moves when the mantle moves beneath it

4 Pieces Evidence 1. Shape of the continents

Continents seem to fit together

Drifting Continents: Alfred Wegerner: Theory of Cont. Drift

2. Fossil Evidence identical fossils found in Africa and South America

suggests continents were closer and connected

- too large to be carried by the wind

- too fragile to survive the ocean - too far between the continents

3. Rock Evidence Rock formations and Coal fields in Africa

line up with matching formations in South America

Folded Mountain chain stretches across South Africa and matches one in Argentina

Similar rocks and structures of the Appalachian Mountains can be found in the British Isles and Scandinavia

4. Climate Glacial deposits found in warm climate

--- therefore: areas were once closer to the poles

Salt deposits in Northern States --- salt forms in tropical regions -- area was once warmer

Explains most geologic processes Evidence of mid-ocean ridges and ocean

floor spreading helps explain continental drift

Links together ideas of continental drift and ocean floor spreading

Explains formations, movements, collision and destruction of the Earth’s crust

Plate Tectonics (1968)

Provides framework for understanding:◦ - Mountains◦ - Volcanoes◦ - Earthquakes

- insights on how & why life on Earth has evolved

- helps understand the past & predict the future

The upper mantle and the crust behave as a strong rigid layer called the lithosphere that is divided into plates

- slow continuous rate of movement – 5 cm/yr

- driven by convection currents in the Earth’s mantle

Earth’s Major Plates

1) Divergent Boundaries – 2 plates moving apart

2) Convergent Boundaries – 2 plates moving together

3) Transform Fault Boundaries – 2 plates that grind (slide) past each other

3 major types of plates

◦the permanent magnetic field of a rock that shows the direction of the magnetic field at the time of the rocks formation

◦when hot, minerals in newly formed rocks align themselves with the earth’s magnetic poles

◦As the Earth’s magnetic poles change so do the direction of the rock’s magnetic poles

1.Paleomagnetism

strips of alternating polarity - mirrored on each side of ocean ridges

Therefore: Each strip that has a different polarity had to be formed at different time – supports sea floor spreading

On the ocean floor

◦A link between deep-focus earthquakes and ocean trenches

◦Shallow earthquakes occur near or at the trench

◦Deep earthquakes occur toward the mainland

2. Earth Quake Patterns

◦Drilling of the ocean floor from the mid ocean ridge toward the coast lines

◦Oldest rocks were found closest to the shoreline, youngest nearest the ridge

◦Therefore: The ridge is producing new oceanic crust while older crust is being pushed toward the shoreline

3. Ocean Drilling

◦Rising magma from the mantle produces volcanoes along the floor of the ocean

◦As plates move, new volcanoes are formed along the floor bottom above the hot spot

◦Hawaii – age of features increase as you move away from the hot spot (Kilauea)

◦Therefore: The plates are moving over the hot spot and forming new volcanic features.

4. Hot Spots

Convection Currents basic driving force◦Hot, less dense magma rises toward the

crust while cooler, more dense magma sinks

◦Plates move because of the uneven distribution of the Earth’s heat

Causes of Plate motion

The pulling of old crust down in the mantle because by the downward flow of more dense magma in the convection current

Slab-pull

The down-ward pull, from gravity, on the oceanic lithosphere at the ridge

Ridge –push

http://www.youtube.com/watch?v=ryrXAGY1dmE