Continental Drift and Plate Tectonics

Crust: - the outermost layer - rigid and very thin km thick - brittle and breakable. Mantle: dense, hot layer of semi-solid rock - 2,900 km thick. Core: - nearly twice as dense as the mantle - mostly metallic (iron-nickel alloy) - two distinct parts: a 2,200 km-thick liquid outer core and a 1,250 km-thick solid inner core.

-The Earth’s interior is very hot from the radioactive decay of certain elements such as uranium, thorium, and potassium.

The Earth's crust is constantly moving, both vertically and horizontally, at rates of up to several inches a year on plates.

Plates? The term "plate" refers to large rigid blocks of the Earth's surface which appear to move as a unit. include both oceans and continents. When the plates move, the continents and ocean floor above them move as well. Continental Drift occurs when the continents change position in relation to each other.

How do you know that? The solid rock moves on a layer of magma. Think about it as liquid rock. Very hot!

Lithosphere: The upper part of the mantle is cooler and more rigid than the deep mantle; in many ways, it behaves like the overlying crust Lithosphere: about 80 km thick. It’s broken up into the moving plates that contain the world's continents and oceans.

Asthenosphere below the lithosphere is a relatively narrow, mobile zone in the mantle hot, semi-solid material, which can soften and flow after being subjected to high temperature and pressure over geologic time. The rigid lithosphere is thought to "float" or move about on the slowly flowing asthenosphere.

Moving Mountains

Who thought of that? Alfred Wegener ( ), a German meteorologist and geologist. First person to propose the theory of continental drift, in his book, "Origin of Continents and Oceans." Discovered Pangaea, a combination of all the continents that was formed 200 million years ago.

How did he think of that?

EVIDENCE OF CONTINENTAL DRIFT The Shapes Match The bulge of Africa fits the shape of the coast of North America while Brazil fits along the coast of Africa beneath the bulge.

The Plants and Animals Match Wegener noted that plant fossils of late Paleozoic age found on several different continents were quite similar.

The Rocks Match Broad belts of rocks in Africa and South America are the same type. These broad belts then match when the end of the continents are joined.

The Ice Matches Wegener was aware that a continental ice sheet covered parts of South America, southern Africa, India, and southern Australia about 300 million years ago. Glacial striations on rocks show that glaciers moved from Africa toward the Atlantic Ocean and from the Atlantic Ocean on to South America.

Convergent Boundaries where crust is destroyed as one plate dives under another. plates are moving toward each other, and sometimes one plate sinks under another. sinking of a plate is called a subduction zone.

When stuff hits: When two continental plates collide = mountains. When a continental plate and an oceanic plate collide = a trench, where one plate subducts. When two oceanic plates collide = a trench, and sometimes volcanoes. When the lava builds up, islands are formed.

Convergent Plates

Divergent Boundaries where new crust is generated as the plates pull away from each other. occur along spreading centers where plates are moving apart and new crust is created by magma pushing up from the mantle. the Mid-Atlantic Ridge.

Divergent Plates Lithosphere Asthenosphere Magma

Divergent Plates

Transform Boundaries where crust is neither produced nor destroyed as the plates slide horizontally past each other. most are found on the ocean floor. generally defined by shallow earthquakes.

Should we put on our swim suits? Average rate = 5 cm/yr = 2 in/yr

As the Earth rotates  Liquid outer core spins  Creating the Earth's magnetic field.

Beginning in the 1950s, scientists, using magnetic instruments (magnetometers) adapted from airborne devices developed during World War II to detect submarines, began recognizing odd magnetic variations across the ocean floor.

Our Magnetic Oceans basalt -- the iron-rich, volcanic rock making up the ocean floor– Magnetite: can locally distort compass readings

The only explanation… is seafloor spreading and recycling of oceanic crust.

Hawaii

Subduction.swf ocean-con ocean-ocean con-con

Sources: calplates3/en/index.shtmlhttp:// calplates3/en/index.shtml mic.html#anchor http://pubs.usgs.gov/publications/text/dyna mic.html#anchor