Forces that act on the Earth

The Inner Core

•The deepest layer in Earth is the inner core. It is located at the center of Earth because it contains the densest material of all the Earth’s layers. The inner core is solid and mostly composed of the element iron (Fe). Its extremely hot temperature is estimated at 6,000 °C. This layer is approximately 1,250 km thick.

The Outer Core

•The outer core is less dense than the inner core and therefore, is located around the inner core. The temperatures range from 4,000°C to 5,000°C. The outer core is approximately 2,200 kilometers thick and is a combination of mostly molten iron (Fe) and nickel (Ni). Molten describes materials that change to liquid form when exposed to extreme amounts of thermal energy.

The Mantle and Asthenosphere

•The mantle is located outside the outer core. This layer is mostly made of iron (Fe) and magnesium (Mg) and has a thickness of approximately 2,900 kilometers. The upper mantle’s high temperatures of 2,800-3,200 °C can melt rock. The semisolid layer in the upper part of the mantle is called the asthenosphere. The asthenosphere is a solid that flows like a liquid. This physical property is called plasticity. Scientists believe that the lithosphere and the crust are able to move slowly over the top of the mantle and asthenosphere.

The Crust and Lithosphere

•The layer around the asthenosphere is known as the lithosphere. The lithosphere is the solid outer layer of earth that consists of the crust and the upper mantle. This layer is made mostly of the element oxygen (O2) and silicon (Si). The crust is the thinnest layer of Earth and is much cooler in temperature. Continental crust is thicker than oceanic crust. The crust is broken into many large pieces called plate tectonics. Scientists believe these plates “float” and move around very slowly on the semi liquid asthenosphere.

Plate Tectonics

Plate Tectonics • Earth’s crust and upper mantle

are broken into sections called plates.

• The plates and upper mantle form a solid layer of the Earth called the lithosphere.

• The plates move on top of the plastic-like section of the mantle called the asthenosphere.

• Areas where plates meet one another are called plate boundaries.

Plate Boundaries

Name of Plate Boundary: Convergent

•What happens here??▫Plates move together

• Landforms created▫Mountains ( c c )

▫Volcanic Mountains (c o)

(Volcanoes)▫Ocean Trench (where oceanic plate

subducts)

▫Volcanic Islands (o o)

Name of Plate Boundary: Divergent

•What happens here??▫Plates move apart

• Landforms created▫Mid-ocean ridges (o o)

▫Rift Valleys (c c)

Divergent Boundary

Name of Plate Boundary: Transform

•What happens here??▫Plates slide past each other

• Landforms created▫Earthquake

Fault – a break in rock. When movement along a fault occurs, earthquakes result.

How Do Plates Move?

How Do Plates Move?

•Heat from Earth’s core and from the mantle itself cause convection currents in the mantle.

•A convection current is created within a liquid or gas when it heats up and cools down.

1. When a liquid or a gas is heated, the particles move faster.

2. As the particles move faster, they spread apart and take up more space. (This causes the density to decrease.)

3. Substances with a lower density will rise up through substances with a higher density. (Think of oil and water)

4. The heated molten material becomes less dense and will rise above the cooler molten material.

5. When the molten material reaches the surface, it begins to cool down and sink back down into the mantle.

Summary1. When a liquid or a gas is heated, the particles move

faster.2. As the particles move faster, they spread apart and take

up more space. (This causes the density to decrease.)3. Substances with a lower density will rise up through

substances with a higher density. (Think of oil and water)

4. The heated molten material becomes less dense and will rise above the cooler molten material.

5. When the molten material reaches the surface, it begins to cool down and sink back down into the mantle.

Label the arrows of the direction of the convection currents

Check your answer.

Plate Tectonics Theory

•Plate Tectonics follows the idea in which the lithosphere is divided into a number of crustal plates, each of which moves on the plastic asthenosphere to collide with, move apart from, or move past adjacent plates.

This cycle continues as the molten material in the mantle heats up and then cools down.These convection currents within the Earth are thought to be the theory behind plate tectonics.

Seafloor Spreading

Seafloor Spreading

•Many years ago, scientists discovered underwater mountain ranges called the mid ocean ridges.

•Plate Tectonics follows the idea in which the lithosphere is divided into a number of crustal plates, each of which moves on the plastic asthenosphere to collide with, slide under, or move past adjacent plates.

In the 1960’s, Harry Hess suggested the theory of seafloor spreading to explain how these ridges were formed.

1. Hot, less dense material below Earth’s crust rises upward to the surface at the mid-ocean ridges.

2. Then, it flows sideways, carrying the seafloor away from the ridges.

3. As the seafloor spreads apart, magma moves up and flows from the cracks, cools, and forms new seafloor.

Summary

1. Hot, less dense material below Earth’s crust rises upward to the surface at the mid-ocean ridges.

2. Then, it flows sideways, carrying the seafloor away from the ridges.

3. As the seafloor spreads apart, magma moves up and flows from the cracks, cools, and forms new seafloor.

Is there evidence that this occurs?Of course!

▫Younger rocks are located at mid-ocean ridges.

▫Reversals of Earth’s magnetic field are recorded by rocks in strips parallel to ridges.

Continental Drift

• It is believed that all continents were once connected as one large landmass known as Pangaea.

The continental drift hypothesis states that continents have moved slowly to their current locations. Alfred Wegener (1912) was the author of this hypothesis.

• In 1596, Abraham Ortelius suggested that the Americas split from Europe and Africa.

Evidence

▫The continents fit together like a puzzle.▫Similar fossils have been found on different

continents.▫The remains of warm-weather plants in

arctic areas and glacial deposits in tropical areas suggest that continents have moved.

▫Similar rock structures have been found on different continents.