Plate Tectonics review The Big Ideas: • Characteristics of tectonic plates • How convection in the mantle drives plate motion • 3 types of plate boundaries and typical features at each boundary SCHS-S6C1-PO1, SCHS-S6C1-PO3, SCHS-S6C2-PO4, SCHS-S6C2-PO5

In 1910 Alfred Wegner, a German meteorologist, begins to wonder… Is there a relationship between all of the continents? Perhaps all the continents pieces used to be connected? Continental drift = slow movement over Earth’s surface Scientists thought Wegner was crazy

Two unanswered questions were the main reasons that the hypothesis of continental drift was rejected. what forces could move continents? how continents could move without shattering?

Plate Tectonics... a unifying theory A. Outer part of Earth consists of thin and rigid pieces called plates, and these plates move slowly and continually. B. 4 main pieces of Evidence: 1. shape of continents = fit together like a puzzle Similarity of fern fossils found on India, Australia and South Africa Similarity of reptile fossils found in South America and Africa Paleomagnetism – where igneous rocks that contain iron record Earth’s magnetic direction at the time the rocks cooled. In a nutshell… bullet 1

Fern fossil evidence

Paleomagnetism evidence

Plate Tectonics... a unifying theory C. Plates: 6 major plates and multiple smaller plates Each plate ~ 100 km thick Moving 1 – 20 cm/year. Average speed is 2 cm/year D. Plate tectonics theory explains the location of mountain ranges, volcanoes, and earthquakes. In a nutshell… bullet 1

Tectonic Map of the World The arrows show which direction the plates are moving. For example, the North American plate is moving in the NW direction. We’re moving! The length of the arrows indicates speed. A long arrow = relatively fast plate movement A tectonic plate is like the hard shell on a boiled egg that has been cracked into pieces or plates.

Earthquake Map of the World The arrows show which direction the plates are moving. For example, the North American plate is moving in the NW direction. We’re moving! The length of the arrows indicates speed. A long arrow = relatively fast plate movement What do you notice?

1. Core – Earth’s internal heat source. 2 sub-layers: Earth’s layers 1. Core – Earth’s internal heat source. 2 sub-layers: a. Inner core: solid iron and nickel Outer core: liquid iron Heat in the core caused from remnant heat from Earth’s formation & radioactive decay of elements.

Earth’s layers 2. Mantle – made of plastic-like magma, 2 sub-layers: a. Asthenosphere – lower mantle, made of iron and magnesium. Is semi-solid and can flow like silly putty. b. Lithosphere – upper mantle, rigid and stiff. Does not flow! c. Asthenosphere and Lithosphere separated by a change in density and rock composition. The boundary between is called the Moho discontinuity.

3. Crust – outer skin of the earth. 2 types of crust: Earth’s layers 3. Crust – outer skin of the earth. 2 types of crust: a. Oceanic – thinner, denser, basalt rock b. Continental – thicker, less dense, granite rock.

Plate composition B. Earth’s plates are made of either oceanic or continental crust and the lithosphere. These tectonic plates “float” on top of the plastic-like asthenosphere.

First 2 minutes

Tectonic Map of the World The arrows show which direction the plates are moving. For example, the North American plate is moving in the NW direction. We’re moving! The length of the arrows indicates speed. A long arrow = relatively fast plate movement But how do the plates move? What causes plate motion?

Answer: convection currents in the mantle how do the plates move? Answer: convection currents in the mantle Convection occurs when a liquid or gas is heated, becomes less dense and rises. When it cools, it gets more dense and sinks, and the process repeats. This cycle of heating and cooling drives plate motion.

Draw this simple convection current

Convection in the asthenosphere

Tectonic Map of the World So, now we know why plates move…but what happens at the plate boundaries? Each plate is in a different color. Notice that the continents and oceans can be on the same plate. Point out North America and Pacific plates.

What happens at the boundaries? Plate Boundary Diagram Description Convergent 2 plates collide into each other. Mountains or subduction zones form. Divergent 2 plates move away from each other. Magma rises to surface. Transform 2 plates slide past each other. Focus on red arrows

What happens when an oceanic plate meets a continental plate? A. SUBDUCTION: Oceanic plate (denser) forced under continental (lighter) plate 1. At the subduction zone a deep sea trench is formed where the plate is being forced downwards under the continental plate. 2. Subduction causes rocks to melt, and magma rises to surface to form volcanoes! 3. Examples: Cascades in US, Andes Mountains in South America.

What happens when a continental plate meets a continental plate? Mountains can be formed when 2 continental plates collide into each other. 1. Because they both have the same density, neither one subducts under the other. They crumple together. 2. Classic examples are the Himalayas, which are still going up! The Himalayas are still growing today at a rate of 1 - 2 cm a year!

Himalayas – 29,029 ft and rising!

What happens when plates pull apart? C. When 2 plate move away from each other, magma rises and new crust is formed. This is happening along the mid-Atlantic ridge, which passes through Iceland. If continental crust pulls apart from continental crust then the same process occurs. As magma erupts to the surface to fill the gap, a volcano is created.

Mid-Atlantic ridge in Iceland Mt. Lemmon is 9,000 ft.

What happens when plates move along side each other? D. When plates move past one another earthquakes occur. Plates are rigid so it is difficult for the plates to slide past each other. The most famous conservative plate margin is the San Andreas Fault on the western coast of North America.

San Andreas fault in CA

Take notes on the next video the BIG picture Take notes on the next video

Crash course- continental drift (https://www. youtube. com/watch <iframe width="560" height="315" src="https://www.youtube.com/embed/KB7HzF2O3Kg" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>

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