Plate Tectonics Evolution of the Earth Free powerpoints at http://www.worldofteaching.com

Interior Inner Core Outer Core Lower Mantle Upper Mantle Crust

Interior 1220 km 2259 km 2851 km

What’s in the Earth’s Layers: Crust: is made up of Silicates which are cooler-rigid rock Mantle: -made up softer weaker rock that can flow slowly. Core: -Outer core: liquid metal and very hot! -Inner core: solid metal and very high pressure!

Volcanoes Volcanoes are the result of hot spots within the crust or mantle of the earth. The hot, liquid rock will break through weak spots in the surface and form volcanoes or flood basalts. These are called Effusive/Quiet Volcanoes Many volcanoes do not release lava, instead they spit ash. These are called Explosive Volcanoes The type of volcano is determined by the materials in it. Go to: http://www.nationalgeographic.com/forcesofnature/interactive/index.html

Volcanoes Fill in the following table to determine how quiet and explosive volcanoes differ: Dissolved Gases Silica Content Type of Volcano Looks like…. Effusive or Explosive High Low

Volcanoes Quiet lava flows

Volcanoes Mt. St. Helen before the explosive eruption

Volcanoes

Volcanoes Time lapse of the eruption

Volcanoes Mt. St. Helen after the eruption

Volcanoes Mt. St. Helens begins the rebuilding process

Flood basalts: When volcanic eruptions coats a thick layer of cooled magma over the surface of the earth. This is IGNEOUS ROCK. Igneous Rock is a type of rock that is made in the mantle

Volcanoes

Where does the energy to make a Volcano come from?

The earth’s core is extremely HOT The earth’s core is extremely HOT! Magma in the mantle is always moving in the earth because of the Earth’s Core, which causes Convection: Hot materials rise and cool materials sink.

This causes the plates to move with the magma of the mantle to: 1) move apart (Divergent Boundaries) or 2) move together (Convergent Boundaries) and even 3) past one another (Transform Boundaries.)

Because Plates move they cause the magma to be released through cracks in the earth’s crust creating volcanoes.

Volcano locations: Why at these locations?

The answer is Tectonic Plates

The reason volcanoes occur at specific locations: 1. Plate Tectonics Move at a Convergent Zone: (together)

Convergent Zones: Volcanoes

The reason volcanoes occur at specific locations: 2. At Divergent Zones: (a part)

Tectonic Plates

Tectonic Plates Another source of evidence is based on seafloor ages which get younger as we approach sea floor ridges

Pangea What is Pangaea? Pangaea was a super continent at one time. Scientists use the similarity of rock types and fossil types that date to the same age to support their theory that the continents were connected to form a super continent. The map below give just one example of areas on different continents that show the same fossils and rock types.

Pangea

Pangea

Pangea The break up of Pangea

The reason volcanoes occur at specific locations: 3. Magma moves to the surface of the earth near a weak spot and can activate a magma chamber http://sio.ucsd.edu/volcano/about/magma.html 4. This can happen over a HOTSPOT. The Hawaiian Islands have formed because a plate moved over a hotspot.

Mid-Plate Hotspots

What types of energy are taking place to have a volcano? Mechanical Energy: Magma moves from the interior earth up to a weak portion in the earth’s crust. Magma also moves out from the volcano. Ash and rock can also move out from a volcano like in a pyroclastic flow. Heat Energy The earth’s core has large amounts of heat that escape at the earth’s surface through a volcano Draw how a volcano works by using words to describe the process such as: magma, crust, mantle, mechanical energy, heat energy

Earthquakes Earthquakes are a result of motion within the earth. This only occurs where the earth is solid and therefore can only occur within about 100 miles of the surface Earthquakes provide the best evidence regarding the interior structure of the Earth.

Earthquakes

Earthquakes

Earthquakes

Earthquakes A. Where the earthquake occurs B. Directly above the earthquake   C. Where the land masses move past one another D. Where the land will either drop down, jet up or change along the fault. E. Waves that move outward causing the shaking movement of the earth.

Waves fall under two categories: P-Waves: occurs when fault moves past each other horizontally, cause a compressed wave. S-Waves: occurs when faults move vertically, causes a wavy wave. * Both display Mechanical Energy!

Both Body Waves and Surface Waves will differ in both S & P Waves:

Seismograph: Measures movement in the earth.

Finding an Earthquake’s Epicenter

Earthquakes occur often!

Earthquakes occur at plate boundaries more frequently Location of worldwide earthquakes

Earthquakes Earthquakes by depth. Notice that the deep earthquakes occur only at subduction zones.

The bigger the magnitude of the earthquake, the more mechanical energy there is. Go to: http://www.nationalgeographic.com/forcesofnature/interactive/index.html Fill out the following table: Bed rock Low Description of Damage High Fault Land fill

Different Forms of Energy In the Earth Mechanical Energy: Energy due to motion Heat energy: energy due to heat Potential energy: energy that is built up but not yet released Kinetic Energy: energy that is occurring (in motion)

Tectonic Plates

Tectonic Plates Today plate boundaries are determined by examining the location of volcanoes and earthquakes. Volcanoes result from the friction (heat) of the plates motion. Earthquakes occur where plate rub against one another

Plate Boundaries Convergent – plates move toward one another Divergent – plates move away from each other Transform – plate moves sideways from each other

Faults occur at these Plate boundaries, where land masses move Faults occur at these Plate boundaries, where land masses move. These faults when moved release energy in the form of an earthquake. There are 3 different faults: 1. Normal Fault: as stress is pulled away on the plates, one land mass slips down. (Divergent Plate boundary)

2. Reverse Fault: as two plates come together one land mass jets up above the other making a hanging wall. (Convergent Plate Boundary) 3. Transverse Fault: occurs as two plates slide past one another. (Transform plate boundary)

Tectonic Plates Volcanoes

Tectonic Plates

Tectonic Plates

Tectonic Plates

Tectonic Plates Another source of evidence is based on seafloor ages which get younger as we approach sea floor ridges

Tectonic Plates Our final piece of evidence is the magnetic record of the ocean floor. This shows the pattern of reversal and we find a near perfect mirror image on opposing sides of the ridge

Tectonic Plates

Tectonic Plates

Tectonic Plates

Composition vs. Motion We can look at the interior of the Earth based on the composition of the rocks or based on the movement

Based on Composition Crust – solid, relatively low density silicate rock Mantle – Semi fluid, denser, mafic (iron and magnesium bearing) rocks Core – Liquid then solid iron and nickel with traces of heavier elements

Plate Types Oceanic plates: basalt Dark (black) and dense rock type composed of silicates, iron and magnesium Continental plates – granite and andesite Light colored (pink, white and gray) and low density rock type composed almost entirely of silicates.

Plate Boundaries

Plate Boundaries

Convergent Plates

Convergent Plates

Convergent Plates

Convergent Plates The only subduction zone in the Atlantic

Convergent Plates Black arrows show subduction zones and the direction of plate movement

Convergent Plates Looking at the depth of earthquakes shows that angle that the plate is being subducted

Divergent Plates

Divergent Plates

Divergent Plates

Divergent Plates

Transform Plates

Mid-Plate Hotspots

Mid-Plate Hotspots

Transform Plates San Andreas Fault

Mid-Plate Hotspots

Mid-Plate Hotspots

Why do the Plates Move?

Why do the Plates Move? No single idea explains everything but we can identify several forces that contribute to the movement of the plates. Slab pull The sinking of the cooled dense oceanic plates pulls on the rest of the plate Ridge rises The material deposited on the top of the ridge slides downs from the rise pushing on the plate Convection Movement within the mantle could be part of the driving force behind the motion of the plates.

The Big Picture

Pangea What is Pangaea? Pangaea was a super continent at one time. Scientists use the similarity of rock types and fossil types that date to the same age to support their theory that the continents were connected to form a super continent. The map below give just one example of areas on different continents that show the same fossils and rock types.

Pangea

Pangea

Pangea The break up of Pangea

Where are we going? We appear to be headed for another super continent as North America, South America, Asia and Australia converge in the ever shrinking Pacific Ocean