introduction to earths surface

ocean basins

The ocean basin begins where the ocean meets the land. The continental margin begins at the shore and goes down to the ocean floor. It includes the continental shelf, slope, and rise. The continental shelf is part of the continent, but it is underwater today. It is about 100-200 meters deep, much shallower than the rest of the ocean. The continental shelf usually goes out about 100 to 200 kilometers from the shore (Figure 2.9). The continental slope is the slope that forms the edge of the continent. It is seaward of the continental shelf. In some places, a large pile of sediments brought from rivers creates the continental rise. The continental rise ends at the Besides seamounts, there are long, very tall (about 2 km) mountain ranges. These ranges are connected so that they form huge ridge systems called mid-ocean ridges (Figure 2.11). The mid-ocean ridges form from volcanic eruptions. Lava from inside Earth breaks through the crust and creates the mountains. The deepest places of the ocean are the ocean trenches. Many trenches line the edges of the Pacific Ocean. The Mariana Trench is the deepest place in the ocean. (Figure 2.12). At about 11 km deep, it is the deepest place on Earth! To compare, the tallest place on Earth, Mount Everest, is less than 9 km tall.

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continents and landforms

If you take away the water in the oceans (Figure 2.6), Earth looks really different. You see that the surface has two main features: continents and ocean basins. Continents are large land areas. Ocean basins extend from the edges of continents to the ocean floor and into deep trenches. Continents are much older than ocean basins. Some rocks on the continents are billions of years old. Ocean basins are only millions of years old at their oldest. Because the continents are so old, a lot has happened to them! As we view the land around us we see landforms. Landforms are physical features on Earths surface. Landforms are introduced in this section but will be discussed more in later chapters. Constructive forces cause landforms to grow. Lava flowing into the ocean can build land outward. A volcano can be a constructive force. Destructive forces may blow landforms apart. A volcano blowing its top off is a destructive force. The destructive forces of weathering and erosion change landforms more slowly. Over millions of years, mountains are worn down by rivers and streams. Constructive and destructive forces work together to create landforms. Constructive forces create mountains and erosion may wear them away. Mountains are very large landforms. Mountains may wear away into a high flat area called a plateau, or a lower-lying plain. Interior plains are in the middle of continents. Coastal plains are on the edge of a continent, where it meets the ocean. Rivers and streams flow across continents. They cut away at rock, forming river valleys (Figure 2.8). These are

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topography

As you know, the surface of Earth is not flat. Some places are high and some places are low. For example, mountain ranges like the Sierra Nevada in California or the Andes in South America are high above the surrounding areas. We can describe the topography of a region by measuring the height or depth of that feature relative to sea level (Figure mountains, while others are more like small hills! Relief, or terrain, includes all the landforms of a region. A topographic map shows the height, or elevation, of features in an area. This includes mountains, craters, valleys, and rivers. For example, Figure 2.5 shows the San Francisco Peaks in northern Arizona. Features on the map include mountains, hills and lava flows. You can recognize these features from the differences in elevation. We will talk about some different landforms in the next section.

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direction

When an object is moving, it is not enough to describe its location. We also need to know direction. Direction is important for describing moving objects. For example, a wind blows a storm over your school. Where is that storm coming from? Where is it going? The most common way to describe direction is by using a compass. A compass is a device with a floating needle (Figure 2.1). The needle is a small magnet that aligns itself with the Earths magnetic field. The compass needle always points to magnetic north. If you have a compass and you find north, you can then know any other direction. See the directions, such as east, south, west, etc., on a compass rose. A compass needle lines up with Earths magnetic north pole. This is different from Earths geographic north pole, or true north. The geographic north pole is the top of the imaginary axis around which Earth rotates. The geographic north pole is much like the spindle of a spinning top. The location of the geographic north pole does not change. However, the magnetic north pole shifts in location over time. Depending on where you live, you can correct for the difference between the two poles when you use a map and a compass (Figure 2.2). Some maps have a double compass rose. This allows users to make the corrections between magnetic north and true north. An example is a nautical chart that boaters use to chart their positions at sea (Figure 2.3).

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location

To describe your location wherever you are on Earths surface, you could use a coordinate system. For example, you could say that you are at 1234 Main Street, Springfield, Ohio. Or you could use a point of reference. If you want to meet up with a friend, you could tell him the distance and direction you are from the reference point. An example is, I am at the corner of Maple Street and Main Street, about two blocks north of your apartment. When studying Earths surface, scientists must be able to pinpoint a feature they are interested in. Scientists and others have a system to describe the location of any feature. Usually they use latitude and longitude as a coordinate system. Lines of latitude and longitude form a grid. The grid is centered on a reference point. You will learn about this type of grid when we discuss maps later in this chapter.

instructional diagrams

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questions

Earths magnetic north pole is always located in the same place.

a. true

-->  b. false

Continents

a. are above sea level

b. are older than ocean basins

-->  c. both a and b

d. none of the above

A compass needle points toward Earths true north.

a. true

-->  b. false

Which of the following is NOT an example of a destructive force?

a. A volcano blowing its top off

b. Rivers cutting away at rocks

-->  c. Rivers bringing sand to the shore to form beaches

d. Wind wearing down mountains to become plateaus

All landforms are created by constructive forces.

a. true

-->  b. false

A double compass rose

a. shows both direction and location

b. is used by sailors

-->  c. shows the difference between true north and magnetic north

d. both b and c are correct

The terrain of an area, or the difference between high and low points in an area, is known as

a. elevation

-->  b. relief

c. height

d. landform differential

A mountain may wear away into a high flat area called a plateau.

-->  a. true

b. false

Examples of landforms include hills, straits, and capes.

-->  a. true

b. false

Constructive forces

a. create new land and features

b. build land outward

c. are responsible for creating mountains

-->  d. all of the above

The ocean basin begins where the ocean meets the land.

-->  a. true

b. false

The continental shelf is the part of a continent that is under ocean water.

-->  a. true

b. false

The continental rise is formed by volcanic eruptions.

a. true

-->  b. false

Mid-ocean ridges form from sediments deposited by ocean water.

a. true

-->  b. false

The Mariana Trench is the deepest place on Earth.

-->  a. true

b. false

Latitude and longitude can describe direction.

a. true

-->  b. false

Elevation describes how far above sea level an object is.

-->  a. true

b. false

Continents can be billions of years old.

-->  a. true

b. false

Mid-ocean ridges are the deepest places in the ocean.

a. true

-->  b. false

The ocean basin begins where the ocean meets the land.

-->  a. true

b. false

difference in elevation of landforms in a region

a. compass

b. compass rose

c. continent

d. elevation

-->  e. relief

f. topography

g. landform

land mass above sea level

a. compass

b. compass rose

-->  c. continent

d. elevation

e. relief

f. topography

g. landform

relief over a given region

a. compass

b. compass rose

c. continent

d. elevation

e. relief

-->  f. topography

g. landform

figure on a map or nautical chart that shows north, south, east, and west

a. compass

-->  b. compass rose

c. continent

d. elevation

e. relief

f. topography

g. landform

height of a land feature measured relative to sea level

a. compass

b. compass rose

c. continent

-->  d. elevation

e. relief

f. topography

g. landform

device with a magnetic needle that is used to find the magnetic north pole

-->  a. compass

b. compass rose

c. continent

d. elevation

e. relief

f. topography

g. landform

physical feature on Earths surface

a. compass

b. compass rose

c. continent

d. elevation

e. relief

f. topography

-->  g. landform

You could use a topographic map to find the

-->  a. elevation of landforms in a region.

b. average temperature of an area.

c. population density of a region.

d. type of vegetation in an area.

Which statement about continents is true?

-->  a. They may have rocks that are billions of years old.

b. They are younger than the ocean basins.

c. They float on ocean water.

d. none of the above

Constructive forces form

a. mountains.

b. river deltas.

c. barrier islands.

-->  d. all of the above

Which of the following can be both a constructive force and a destructive force?

-->  a. volcanic eruption

b. weathering

c. erosion

d. two of the above

The continental margin includes the continental

a. shelf.

b. slope.

c. rise.

-->  d. all of the above

The abyssal plain makes up much of the

a. interior of continents.

b. deep-ocean trenches.

-->  c. floor of the ocean.

d. mid-ocean ridges.

The deepest places in the ocean are

a. continental slopes.

b. mid-ocean ridges.

c. seamounts.

-->  d. trenches.

diagram questions

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