PLATE TECTONICS Why the Earth is Like It Is

Earth Layers Earth is made up of 5 layers: 1.Inner Core 2.Outer Core 3.Mantle 4.Asthenosphere (Lower and middle mantle) 5.Lithosphere (Upper mantle and crust)

The crust is thin, varying from a few tens of kilometers thick beneath the continents to less than 10 km thick beneath the many of the oceans. The crust and upper mantle together constitute the lithosphere, which is typically km thick and is broken into large plates. The plates sit on the asthenosphere.

Plate tectonics is the theory that Earth's outer layer is made up of plates, which have moved throughout Earth's history. The theory explains the how and why behind mountains, volcanoes, and earthquakes.

Continental Drift Continental Drift: Alfred Wegener's theory that all continents were once connected in a single, large landmass (called Pangaea) that broke apart about 200 million years ago and drifted slowly to their current positions.

What Did The Earth Look Like In The Past?

What evidence do we have that the continents have moved? Fossil Clues : Fossils of similar plants and animals have been found on continents that are now very far apart, but were perhaps once joined together. Climate clues: Evidence of glaciers can be found on land that is now tropical, because that land was once located in a colder region of our planet. Rock Clues: Similar rock structures can be found on continents that are now far apart, again suggesting that they could have once been joined. Rocks found in the eastern US are similar to those found in western Europe.

Major Tectonic Plates: Tectonic Plates World Map Tectonic Plates World Map (link)

Do land features continue to change? Are the continents still moving? The earth’s tectonic plates continue to gradually move even today. The plates interact. Where one plate meets another, is called a boundary.

How do we know? Hot Spots (Hawaii, Yellowstone) Volcanoes and Earthquakes Ring of Fire – very active region of subduction

Why Do Plates Move? Plates are “pushed” and “pulled” over the surface of the Earth due to unbalanced forces. When convection currents reach the surface, plates are pushed apart As the plates move away from each other, part of them are pulled into the Earth’s mantle

Convection Currents The mantle "flows" because of convection currents. Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling and sinking again --repeating this cycle over and over.

Plates Move Toward Each Other This is called Convergent Boundary – these are destructive boundaries since they deform the plates Continent/Continent Ocean/Continent Ocean/Ocean

Convergence creates mountains Most volcanoes (but not all) form along Convergent boundaries, as one plate is pushed under another and the old crust melts. As two plates rub against one another, a number of small and large earthquakes could occur near convergent boundaries.

Convergence – Moving Together Trenches Mountains Structural Mountains Volcanic Mountains

Plates Move Away From Each Other This is called Divergence – these are constructive boundaries since they produce new land Africa and Arabia North America and Eurasia Mid-Atlantic Ridge

Divergent Boundaries Most often takes place at ocean ridges. As the two sides of the crust move away from each other, magma wells up from the Earth's interior. It then solidifies into rock as it is cooled by the sea, creating new ocean floor. Causes some volcanoes and earthquakes to form.

The ridges are zones of intense volcanic activity. In addition to forming at the bottom of oceans, these divergent boundaries can also form on continents. When this happens, a line of volcanoes emerges.

Rift Valley – if the land is above water Sea Floor Spreading – when the land is below water Divergence – Moving Apart

The San Andreas Fault is undoubtedly the most famous transform boundary in the world. To the west of the fault is the Pacific plate, which is moving northwest. To the east is the North American Plate which is moving southeast. Plates Move Side By Side - ***SHIFTING This is called Transform Boundary – Transform boundaries neither create nor consume crust. Rather, two plates move against each other, building up tension, then releasing the tension in a sudden and often violent jerk. This sudden jerk creates an earthquake.

San Andreas Fault Is a continental transform fault that runs a length of roughly 1,300 km (800 miles) through California.

Review clip Review clip (click on the link above)

Review Divergent : Boundary between two plates that are moving apart. Convergent : Boundary between two plates that are pushing together. Transform (Strike-slip) : Boundary between two plates that are sliding past one another. *** Causes Earthquakes Subduction Zone: The area where one plate pushes down under another. Volcanoes are often created by this.

As two continental plates move toward each other, what landforms would you expect to see? A. Volcanoes B. Cliffs C. New Land D. Mountains

As two continental plates move toward each other, what landforms would you expect to see? A. Volcanoes Incorrect These form at edges of plates or over hot spots

As two continental plates move toward each other, what landforms would you expect to see? B. Cliffs Incorrect These are erosional landforms or minor uplift areas

As two continental plates move toward each other, what landforms would you expect to see? C. New Land Incorrect Forms when plates move apart

As two continental plates move toward each other, what landforms would you expect to see? D. Mountains – correct - because 2 continental masses will push into each other and “crumple” the edges to form mountains

Where would you find the newest land on Earth? A. In areas of continental convergence B. In areas where two ocean plates come together C. In areas where plates are moving apart D. In areas where two plates are sliding past each other

Where would you find the newest land on Earth? A. In areas of continental convergence Incorrect Mountains would form here from existing land.

Where would you find the newest land on Earth? B. In areas where two ocean plates come together Incorrect You would find trenches in this area.

Where would you find the newest land on Earth? D. In areas where two plates are sliding past each other Incorrect You would find land movement but not new land being formed

Where would you find the newest land on Earth? C. In areas where plates are moving apart Correct When plates move apart it is due to magma reaching the surface. When magma cools new land is formed.