Chapter 1 plate tectonics power point

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The Changing Earth Chapter 1: Plate Tectonics

Transcript of Chapter 1 plate tectonics power point

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The Changing Earth

Chapter 1: Plate Tectonics

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Section 1.1

Earth Has Several Layers

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Earth is made up of materials with different densities.

Theory: Earth began as a spinning mass of rocks and dust 5 (16?) billion years ago.

Explosions from comets and asteroids, and pressure of Earth’s gravity, produce enough heat to melt materials inside Earth.

Dense material sank to the Earth’s center, less dense material moved toward the surface, forming Earth’s layers.

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Earth’s layers have different properties.

Earth’s LayersLayer Compositio

nTemperatu

re Thickness

Inner Core solid metals 7000-8000°C

2400 km diameter

Outer Core liquid metals 4400-6100 °C

2300 km thick

Mantle heated rock 870-4400 °C 2900 km thick

Crust Cooler rock 0-700 °C 6-70 km thick

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Continued

Earth’s crust and the top of the mantle form the lithosphere.

The lithosphere sits on a layer of hotter, softer rock in the upper mantle called the asthenosphere.

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The lithosphere is made up of many plates.

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Continued

The lithosphere is split into large and small slabs of rocks called tectonic plates, which fit together like a jigsaw puzzle.

Most large plates contain both continental and oceanic crust.

Tectonic plates provide evidence of continental movement that supports the theory of Pangaea.

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Section 1.2

Continents Change Position Over Time.

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Continents join together and split apart.

Alfred Wegener proposed the theory of continental drift in early 1900’s All continents were once joined and

gradually moved apart (still moving). Fossils, studies of ancient climates, and

rock formations provide evidence. Africa and Brazil have matching rock

formations indicating they were once joined.

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Wegner’s theorized that all the continents

were once a single landmass.

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Wegner used fossil evidence to support his continental drift theory.

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The theory of plate tectonics explains how plates and their

continents move.

Wegener’s theory and sea floor maps were used to develop the theory of plate tectonics.

Along spreading centers in the sea floor, melted rock rises through cracks, cools, and forms new crust that builds up mid-ocean ridges.

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Continued: Mid Ocean Ridge at Spreading Center

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Continued

Old crust gets pushed aside and the sea floor slowly spreads apart.

Earth DOESN’T get larger because oceanic crust is destroyed along deep-ocean trenches, where the oceanic plates sink into the asthenosphere.

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Section 1.3

Plates Move Apart

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Tectonic plates have different boundaries.

Plate boundary: where the edges of two plates meet Divergent Boundary: occurs where plates

move apart, usually found in the ocean Convergent Boundary: occurs when

plates push together. Transform Boundary: occur when plates

scrape past each other.

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Divergent Boundary

Convergent Boundary

Transform Boundary

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The sea floor spreads apart at divergent boundaries.

Mid-ocean ridges and rift valleys occur at divergent boundaries in the ocean. Mid-ocean ridges form the longest

mountain ranges on earth. Most contain a rift valley along their

center.

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Continued

Earth’s magnetic poles have switched places several times.

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These magnetic reversals are caused by changes in Earth’s magnetic fields. Bands of rock record periods of magnetic

reversals. As molten material cools, magnetic minerals line up with the magnetic field. When it hardens, the minerals act like

tiny compass needles.

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Continents split apart at divergent boundaries.

Divergent boundaries on continents produce rift valleys.

Magma rises through cracks and forms volcanoes.

As rift valleys grow wider, continents split apart. If the valley continues to widen, the thinned

floor sinks below sea level. It may fill with water to form a sea or lake.

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Hot spots can be used to track plate movements.

Hot Spot: an area of volcanic activity that develops above where magma rises in a plume from the mantle. Can be used to measure plate movement

because it generally stays in one place as the tectonic plate above it moves.

Can provide a fixed point for measuring the speed and direction of plate movements.

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The Hawaiian islands are located in the middle of the Pacific Plate. The largest island, Hawaii,

is still over the hot spot.

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When the plate moves on, it carries the first volcano away from the hot spot. Heat from the mantle plume will then

melt the rock at a new site, forming a new volcano.

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Section 1.4

Plates Converge or

Scrape Past Each

Other.

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Tectonic plates push together and form three

types ofconvergent boundaries.

Continental-continental collision: Two continental plates collide, crumpling and folding the rock between them. Mountains could form.

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Continued

Oceanic-oceanic subductions: two oceanic plates collide and the older, denser plate sinks beneath the top plate, forming deep-ocean trenches and island arcs.

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Continued

Oceanic-continental subductions: an oceanic plate sinks beneath a continental plate, forming a deep-ocean trench and volcanic coastal mountains.

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Tectonic plates scrape past each other at transform

boundaries. Two plates move

past each other in opposite directions.

No crust is formed or destroyed.

Occurs on the sea floor and on land.

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The San Andreas Fault is a transform

boundary and moves about 1 inch per year.

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Boundaries are formed when

tectonic plates move. The

direction of the movement

determines the type of

boundary.

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Comparing BoundariesDivergent *plates move apart *in ocean and

on land *produce mid-ocean ridges, rift valleys, volcanoes, earthquakes

Transform *plates move past each other in opposite directions *in ocean and on land

Convergent C-C Collision

*crumples and folds crust * produces mountains, earthquakes

Convergent O-O Subduction

*older, denser plate sinks *produce deep-ocean trenches, island arcs

Convergent O-C Subduction

*oceanic plate sinks under continental plate * forms deep-ocean trench, volcanic coastal mountains

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The theory of plate tectonics helps geologists today.

The plate tectonics theory enables geologists to understand how Earth’s continents and ocean basins formed.

Helps scientists predict earthquakes and volcanic activity.