Integrated Science One

Plate Tectonics

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Main Layers of Earth

• Crust

• Mantle

• Core

Lithosphere includes the crust and upper mantle

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1. Crust

• This is the skin of the earth

• Only between 8 and 67 kilometers thick

• It is deepest beneath mountains

• Oceanic crust is thinner and more dense than continental crust

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Types of Crust

• Oceanic crust is dense and found beneath the oceans and has a thickness of about 4-7km.

• Continental crust is thicker and less dense and has an average thickness of approximately 20-40 km.

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2. Mantle

• Beneath the crust

• Heavier than the crust

• Between 2800 and 3000 km thick

• Seems to be in a fluid state

• Makes up about 80% of the Earth’s volume

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3. Core

• Beneath the mantle

• Made up of 2 parts– Outer core which contains melted iron and

nickel– Inner core which is hot and solid

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Differences in the 3 main layers

• Crust and mantle are both made of hard solid rock, but the crust is less dense than the mantle.

• The core is believed to be composed of iron and nickel

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Alfred Wegener

• He proposed that based on physical evidence from coastlines, rocks, and fossils the continents were all connected approximately 200 million years ago in a supercontinent called Pangaea.

• This theory is called continental drift

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• One hypothesis states that plate movement results from convection currents in the asthenosphere

• Asthenosphere – the zone of the mantle beneath the lithosphere that consists of slowly flowing solid rock

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Plate Tectonics

• Theory stating that crustal plates on the surface of Earth are continuously moving due to convection currents.– Types of movement of plates

• Divergent• Convergent• Subduction• Transform fault

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Occurances at boundaries of plates

• Earthquakes

• Volcanoes

• Mountain formation

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Divergent boundary

• Occurs where two plates move away from each other

• Forms rift valleys in oceanic crust

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Convergent Boundary

• Where two plates move toward each other

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Transform fault

• Occurs where two plates move past each other

• Breakage of rocks along a fault line releases energy in the form of seismic waves producing earthquakes

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Earthquakes

• Occur at transform faults

• Seismograph measures how much the surface of Earth moves during an earthquake

• Surface waves are the most damaging

• Minimum number of seismograph stations needed to determine earthquake’s epicenter is three

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More on Earthquakes

• The magnitude of earthquakes is expressed using the Richter scale

• The Richter scale expresses the relative magnitude of an earthquake, which is a measure of the energy released at the focus of an earthquake

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Subduction zone

• Zone where oceanic crust dives beneath continental crust

• In subduction zones, when a denser plate dives into the mantle, the rock reaches its melting point and begins to melt and form magma – hot, low density magma rises to surface forming mountains and volcanoes

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Volcanoes

• A vent in Earth’s crust through which hot, liquid rock come to the surface

• Magma released from volcanoes is molten rock from the mantle and crust

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• Volcanoes are common around the edges of the Pacific Ocean because as the Pacific Plate is subducted under surrounding plates, the Pacific Plate is forced into the mantle, where the rock melts and rises to the surface, creating volcanoes

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Types of Volcanoes

• Shield – rich in magnesium and iron

• Cinder – caused by large amounts of gas trapped in the magma

• Composite – composed of many layers of cinders and lava

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Rock Types

• Igneous –

• Sedimentary –

• Metamorphic – changed by heat and pressure. Sedimentary can change into metamorphic

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Igneous

• Formed from magma cooling

• Those that have mineral crystals easily seen with the unaided eye formed intrusively (geode)

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Sedimentary

• Formed by weathering

• Named according to size of the fragments they contain

• Can contain fossils

• Limestone (a sedimentary rock) can be metamorphosed into marble

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Metamorphic

• Rocks that are changed by heat and pressure will form this type of rock– When heated, both igneous and sedimentary

rock become metamorphic

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Age of rocks

• Superposition is used to determine the relative age of rocks

• Radioactive isotopes are used to determine a more exact age of rocks

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New evidence supporting theory of plate tectonics

• Bands of rock with alternating magnetic polarities were discovered on either side of the Mid-Atlantic Ridge in the 1960s. As the youngest rock appears near the center of the ridge and the oldest rock appears further away, this suggests that the oceanic plates are moving away from the plate boundary

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Weathering of rocks

• Physical weathering does not alter the chemical compositon of rock

• Water is the most effective agent of physical weathering and erosion

• The process in which sediment is laid down is called deposition

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Weathering

A. Physical - breaks rock into smaller pieces

1. ice

2. plants

B. Chemical

1. carbon dioxide dissolved in water can dissolve rock

2. acid rain can dissolve minerals

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Essay Questions – choose 1

• How does a seismograph work?

• The Himalayas are a mountain range in India that continues to increase in both width and height. Describe the type of plate boundary found in this region and explain the reason behind the formation of the mountain range

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Erosion

II. Erosion - process by which rock and /or the products of weathering are removed.

A. Water

B. Wind

C. Glaciers

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• How do seismograms recorded during earthquakes help scientists learn about the composition of Earth?

• In an earthquake-prone area, which earth material – igneous rock or sedimentary rock – would be better for constructing buildings? Explain your answer.

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