Earth Science - Chapter 4 - Plate Tectonics

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How do geologists gather evidence about earths interior?

Geologists use seismic waves, they record the seismic waves and study how they travel through Earth to gather evidence about earths interior.

What are the layers that make up the earth?

The Crust - Earths solid and rocky outer layer (oceanic, continental plates)
The Mantle - almost halfway through Earth (lithosphere, asthenosphere)
The Outer Core - layer of molten metal that surround the inner core (liquid)
The Inner Core - a dense ball of solid metal (solid)

What happens in Earths interior to produce Earths magnetic field?

Currents in the liquid outer core force the solid inner core to spin at a slightly faster rate than the rest of the planet. These currents in the outer core also create Earths magnetic field.

What makes up the crust, mantle, core?

Crust - Earths solid and rocky outer layer
Mantle - lithosphere, asthenosphere (made up of molten material)
Core - Inner Core (solid metal) , Outer Core (liquid metal)

What are the three types of heat transfer?

radiation, convection, conduction

Describe how convection currents form.

The heating and cooling of the fluid, changes in the fluids density, and the force of gravity combine to set convection currents in motion.

In general, what happens to the density of a fluid when it becomes hotter?

The density of a fluid decreases when it becomes hotter.

What happens to convection currents when a fluid reaches a constant temperature?

When convection currents reach a constant temperature it stops circulating.

What will happen to the flow of hot rock in Earths mantle if the planets core eventually cools down?

All movement will stop if the planets core eventually cools down

What was Wegner's theory of continental drift?

All the continents had once been joined together in a single landmass and have since drifted apart.

How did Wegner use evidence based on fossils to support his theory that the continents had moved?

Fossils of reptiles have been found in places now seperated by oceans. It is therefore likely that these reptiles lived on single landmass that has once split apart, Wegner used these examples to support his theory that the continents had moved.

What was the main reason scientists rejected Wegner's theory of continental drift?

Wegner couldn't provide a satisfactory explanation for the force that pushes or pulls the continents. Because Wegner couldn't identify the cause of continental drift, most geologists rejected his idea.

What is the role of the mid-ocean ridge in sea-floor spreading?

At the mid-ocean ridge, molten material rises from the mantle and erupts. The molten material then spreads out, pushing older rock to both sides of the ridge.

What is evidence for sea-floor spreading?

Evidence for sea-floor spreading is from molten material, magnetic stripes, and drilling samples.

Describe the process of subduction at a deep-ocean trench?

The process of which the ocean floor sinks beneath a deep-ocean trench and back into the mantle.

Where would you expect to find the oldest rock on the ocean floor?

Closest to the continents.

What is the theory of plate tectonics?

The theory of plate tectonics explains the formation, movement, and subduction of Earth's plates.

What major event in Earth's history began about 225 million years ago?


The Earth's ________ is made of Basalt and granite.


The spinning of the ___________, made of iron and nickel, explains why Earth has a magnetic field.


_____________ form because of differences of temperature and density in a fluid.

Convection currents

_____________ on the ocean floor are places where oceanic crust sinks back to the mantle.

Magnetic stripes

When two continental plates _________, a rift valley forms.


How is the inner core different from the outer core?

inner core is solid and the outer core is liquid.

Why are there convection currents in the mantle?

The heating and cooling fluid, changes in the fluid's density, and the force of gravity combine to set convection currents in motion.

What evidence of Earth's climate in the past supports the theory of continental drift?

The tropical plants, glaciers, and fossils

What was the importance of the discovery that molten rock was coming out of cracks along the mid-ocean ridge?

Closer to the mid-ocean ridge there were newer rocks and closer to the continents were where older rocks are found.

How do magnetic stripes form on the ocean floor? Why are these stripes significant?

Sea-floor spreading makes the magnetic stripes. They are significant because the hold records of reversals in Earth's magnetic field.

What happens when a plate of oceanic crust collides with a plate of continental crust?

The oceanic plate begins to sink and plunges beneath the continental plate.

Oceanic crust is denser then Granite


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