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Interactive Lessons

Standards Covered

8. Describe how wind, water and ice shape and reshape Earth’s land surface by eroding rock and soil in some areas and depositing them in other areas producing characteristic landforms (e.g., dunes, deltas, glacial moraines).
9. Identify and describe how freezing, thawing and plant growth reshape the land surface by causing the weathering of rock.
10. Describe evidence of changes on Earth’s surface in terms of slow processes (e.g., erosion, weathering, mountain building, deposition) and rapid processes (e.g. volcanic eruptions, earthquakes, landslides).

Unit C Chapter 6 Lesson 5

What lies below Earth’s thin surface? Earth cannot be cut open to see the inside. Information can be obtained in several different ways. One way scientists learn about Earth is by studying earthquakes. Earthquakes are movements or vibrations in Earth. Scientists “listen to” and “feel” Earth’s movements by using instruments called seismographs. A seismograph detects, measures, and records the energy of earthquake vibrations.

Pressure within Earth can cause rocks in its outer layer to break. If the rocks along a break move, the break is called a fault. The place where movement begins is called the focus. The focus may be 700 kilometers (about 450 miles) below Earth’s surface.

When an earthquake begins, pressure causes rocks to break and move. Energy is released as vibrations called seismic waves. Seismic waves travel out from the focus in all directions. The waves move through Earth and are felt as shakings and vibrations. The farther waves travel from the focus, the weaker they become. Seismographs in different places record the strength of the waves. By comparing these records, scientists can track waves and determine their speed and direction of travel.

There are several different kinds of seismic waves. Scientists who study these earthquake waves have learned that the waves travel at different speeds through solids, liquids, and gases.

Primary waves, called P waves, are the fastest seismic waves. Secondary waves, called S waves, travel more slowly than P waves. Surface waves, or L waves, are the slowest of the three. L waves cause the damage that often comes from an earthquake.

Scientists have used information from earthquakes to find out what Earth is like on the inside. The solid outer layer of Earth is the crust. This layer is deeper under continents than under oceans. The mantle is the layer of rock lying below the crust. Rocks in this region can move or flow slowly because of great pressures and high temperatures. The outer core is a liquid layer of Earth that is probably made of melted iron. It lies below the mantle. The inner core is a sphere of solid material at Earth’s center.

The information that scientists get from instruments to learn about an earthquake can help them warn people of a possible earthquake.

Unit C Chapter 6 Lesson 4

Soil is made of tiny rock particles, minerals, air, water, and humus. Humus is leftover decomposed plant and animal matter.

It takes hundreds to thousands of years to form one inch of soil. Soil forms in different layers. A layer of soil differing from the layers above it and below it is called a horizon. Topsoil is the top layer of soil. Topsoil is usually dark in color. It is rich in humus and minerals. Most plants grow in this part of the soil.

The layer of soil below the topsoil is known as the subsoil. Subsoil is a fairly hard layer. It is made of clay and minerals. Subsoil is usually light in color. Some plant roots may grow down into the subsoil. Pieces of broken bedrock make up the layer below the subsoil. The different soil horizons make up a soil profile. A soil profile is a vertical section of soil from the surface down to bedrock.

There are many different kinds of soils. Each one has its own set of properties. Different soils have different-sized particles. The particles may have been formed from different kinds of bedrock. The amount of humus in soil depends on the organisms living in the area where the soil was formed. Soils may contain different minerals. Plants use up minerals as nutrients to make their own food. Areas with many plants may have few minerals in the soil.

Soils also differ in permeability, the rate at which water can pass through a material. The spaces between soil particles are called pore spaces. Water and air fill these spaces. Sandy soils have many spaces in them, so they have a high permeability. These kinds of soils hold little water. Soil permeability is important to plants. If the water moves quickly through the soil, it goes beyond the reach of the roots. The water also dissolves minerals in the soil and carries them away. Fine soils are not very permeable. Water soaks in slowly and may remain for a long period of time.

Soil is an important resource. It supplies us with food. Soil is a living system because it is the home for many organisms. People protect soil because it is sensitive to changes in water, temperature, and human activity.

Unit C Chapter 6 Lesson 3

A glacier is a large mass of snow and ice that moves downward and outward over the land. Glaciers form when more snow falls in the winter than melts in the summer. The snow collects in layers. The weight of the upper layers turns the snow to ice. Glaciers move or flow downhill. Heat from friction and Earth melts some of the bottom layer of ice. The thin layer of water helps the glaciers move.

Rock debris collects at the terminus of a glacier. The terminus is the end, or outer margin, of a glacier. When a glacier melts, the rock debris is left behind. This rock debris which is carried and deposited by a glacier is called moraine. Moraines are made up of glacial till, an unsorted mixture of rock materials deposited as a glacier melts.

The rock fragments in glaciers grind away bedrock. They may carve deep scratches and can smooth and polish the rock below them. Generally, glaciers flatten the land and round sharp peaks. Some glaciers carve valleys, making them deeper and U-shaped. Isolated boulders left behind by a glacier are called erratics. Gravel, sand, and clay carried from glaciers by melting water and streams are outwash plains.

In the past, glaciers covered large parts of the world. Periods of very cold temperature, called ice ages, produced many glaciers. Periods of warmer weather existed between ice ages.

Glaciers are not the only things that change Earth’s surface. Wind, waves, running water, and gravity also change the surface. As wind blows, it picks up small particles of dust, soil, and sand. Rock in the path of these winds is worn down as if rubbed by sandpaper. Ocean waves break rock into smaller pieces. Waves also pull materials away from the shore.

Running water causes the greatest change to Earth’s surface. Water flows across the land and picks up particles of rock and soil. The water drops the particles in places far away from where they were picked up. Gravity causes rocks, boulders, soil, and mud to move from a higher place to a lower place. Landslides and mudflows are caused by gravity.

Knowing about glaciers helps us understand how they change Earth’s landscape.

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