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PLATE TECTONICS. Chapter 5. How do we study the Earth’s interior?. Geologist use 2 main types of evidence to learn about the Earth’s interior Direct evidence from rock samples Indirect evidence from seismic waves. Direct evidence from rock samples. Drilling holes deep into
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PLATE TECTONICS Chapter 5
How do we study the Earth’s interior? • Geologist use 2 main types of evidence to learn about the Earth’s interior • Direct evidence from rock samples • Indirect evidence from seismic waves
Direct evidence from rock samples Drilling holes deep into the earth give geologists clues about the interior. Volcanoes also blast rocks from within the Earth that may be studied.
Indirect evidence from seismic activity. When earthquakes occur geologists look at recorded seismic waves and can determine the type of material that makes up the earth’s Interior by looking at the speed of the traveling waves and the paths they take.
The Earth is made up of three main layers. • The three main layers: • Crust • Mantle • Core
Two factors change regularly as you go towards the center of the Earth. • Temperature: In general, temp goes Up steadily • Pressure: Pressure increases the deeper into the earth Y ou go.
THE CRUST The thinnest layer of the Earth. (5 – 40 km thick) Includes the soil & water that covers the earth. Two types of crust: • Oceanic crust – mainly basalt (thinner) • Continental crust – mainly granite (thicker)
The Mantle Nearly 3,000 km thick Made of the Upper Mantle and the Lower Mantle. Upper Mantle has 2 layers: • Lithosphere – like the crust; solid, rigid layer • Asthenosphere - less rigid; can bend like plastic; hotter Lower Mantle is solid all the way to the core.
The Core The core is made up mostly of Fe and Ni. There are two layers: • Outer core – liquid metal • Inner core – dense, solid metal Scientists believe the liquid outer core moves and creates the Earth’s magnetic field.
Convection & The Mantle(Section 2) Before you can understand some of the processes on and in the earth, you must understand heat transfer. There are 3 types of heat transfer: 1) Radiation 2) Conduction 3) Convection
Radiation Radiation is the transfer of heat energy through space. Sunlight is radiation.
Conduction Conduction is heat transfer through the actual contact of two objects. The hotter object transfers heat energy to the cooler object.
Convection Heat energy that is transferred through the movements through liquid or air. It is caused by the differences in temperature which cause differences in density. The hotter something is the LESS dense it is. The colder it is the MORE dense it is. Hot air rises. Think about hot air balloons!
Convection currents in the Earth The extremely hot outer core heats up the lower mantle which heats up the more mobile/tar-like asthenosphere. This hot rock rises then cools and sinks back down. This heating then cooling cycle creates a current within the Earth’s mantle.
The same thing happens when you heat water in a pot!
Drifting Continents In 1910, a scientist named Wegener, proposed that all the continents were once joined together in a single land mass and drifted apart over millions of years. PANGAEA – the supercontinent His theory became known as continental drift. He based his theory on several sources of evidence.
Wegener’s Evidence Wegener studied 3 main areas that supported his continental drift theory. 1) Land Features 2) Fossils 3) Climate change
The Evidence Land features: Mtn ranges on South Amer. and Africa line up when they are pieced together and coal fields in Europe & North Amer line up. Fossils: Ancient fern fossils have been found in all continents including Antarctica!
More evidence…. Climate: In warmer climates certain foliage flourishes that could not grow in much colder environments. Wegener found fossils of tropical plants on an island in the Arctic Ocean. There was also evidence of glaciers once covering South Africa! South Africa was once close to a much colder climate according to Wegener’s theory.
Seafloor Spreading (sect 4) • In all oceans on Earth there is a series of Mid-Ocean Ridges. They are like a mountain system underwater.
Seafloor Spreading (cont) • Seafloor spreading is a process by which the sea floor spreads apart along both sides of a mid ocean ridge adding new crust to the ocean floor.
Evidence of Seafloor Spreading • Molten material found at the ridges from lava erupting. • Magnetic stripes – iron pieces in molten rock align themselves according to earth’s poles and harden as the lava cools. It is a permanent record of earth’s magnetic history.
More evidence • Drilling – rock samples were taken from each side of the ridges and ages were determined. Youngest rocks found near center of ridge and oldest rocks found farther away from the ridges on either side.
New crust is being made but the Earth is not getting bigger! • If the Earth is staying the same size, and new crust is being made, that means somewhere, crust is being removed or recycled! • This happens by a process called: SUBDUCTION
SUBDUCTION • Subduction – happens at deep ocean trenches. This is where the ocean floor sinks back into the mantle. • Seafloor spreading and subduction work together!
Some facts: • The ocean floor is renewed every 200 million years! • The Pacific Ocean is shrinking and the Atlantic Ocean is expanding. • In Pacific Ocean crust is being swallowed up faster (subducting) than it is being made at the ridges.
PLATE BOUNDARIES • 3 TYPES OF BOUNDARIES: 1) Divergent – two plates moving apart Like what happens at mid ocean ridges! Crust is created! 2) Convergent – two plates come together or converge! Some crust is destroyed! 3) Transform – when two plates slip past each other moving in opposite directions. Crust is not created or destroyed!
Divergent Boundary Transform Boundary Click the flag to see animations! Convergent Boundary
Plate Tectonics • This theory explains the formation, movement and subduction of the Earth’s plates.
Convergent Boundary • Here is a convergent boundary between two plates at the Himalayan Mountain Range. The mountains are getting taller! One plate is going under the other making the top plate higher!
Divergent Boundary In Iceland, there is a divergent plate boundary right through the middle of the country!
Transform Boundary • Where the Pacific plate and the North American plate meet is a transform boundary. • Many earthquakes happen at transform boundaries!
