Ch. 2 Lesson 2
A Changing World
Forces of Change
How was the surface of the earth formed?
Since Earth was formed, the surface of the planet has been in constant motion. Landmasses have shifted and moved over time. Landforms have been created and destroyed. The way Earth looks from space has changed many times because of the movement of continents.
A continent is a large, continuous mass of land. Continents are part of Earth’s crust. Earth has seven continents: Asia, Africa, North America, South America, Europe, Antarctica, and Australia. The region around the North Pole is not a continent because it is made of a huge mass of dense ice, not land. Greenland might seem as big as a continent, but it is classified as the world’s largest island. Each of the seven continents has features that make it unique. Earth’s crust is not a solid sheet of rock. Earth’s surface is like many massive puzzle pieces pushed close together and floating on a sea of boiling rock
Earth’s rigid crust is made up of 16 enormous pieces called tectonic plates Heat from deep within the planet causes plates to move Earth’s plates move as much as a few inches each year. This might not seem like much, but over millions of years, it causes the plates to move thousands of miles. Forces within Earth push the edge of one plate up over the edge of a plate beside it. This dramatic movement can create mountains, volcanoes, and deep trenches in the ocean floor. plates are crushed together in a way that causes the edges of both plates to crumble and break. This event can form jagged mountain ranges If plates on the ocean floor move apart, the space between them widens into a giant crack in Earth’s crust. Magma rises through the crack and forms new crust as it hardens and cools. If enough cooled magma builds up that it reaches the surface of the ocean, an island will begin to form.
How Mountains are Formed Activity
Change to Earth’s surface also can happen quickly. Events such as earthquakes and volcanoes caused by plate movement can destroy areas in minutes When two plates grind against each other, faults form. A fault results when the rocks on one side or both sides of a crack in Earth’s crust have been moved by forces within Earth Earthquakes are caused by plate movement along fault lines.Earthquakes also can be caused by the force of erupting volcanoes.
A curipod slide
Various plates lie at the bottom of the Pacific Ocean. These include the huge Pacific Plate along with several smaller plates. Over time, the edges of these plates were forced under the edges of the plates surrounding the Pacific Ocean. This plate movement created a long, narrow band of volcanoes called the Ring of Fire. A tsunami is a giant ocean wave caused by volcanic eruptions or movement of the earth under the ocean floor. Tsunamis have caused terrible flooding and damage to coastal areas.
Earth’s surface plates are moving. Why don’t we feel the ground moving under us?
Other Forces at Work
How can wind, water, and human actions change Earth’s surface?
What happens when the tide comes in and washes over a sand castle on the beach? The water breaks down the sand castle. Similar changes take place on a larger scale across Earth’s lithosphere. These changes happen much slower—over hundreds, thousands, or even millions of years.
Some landforms are created when materials such as rocks and soil build up on Earth’s surface. Other landforms take shape as rocks and soil break down and wear away over time Weathering is a process by which Earth’s surface is worn away by forces such as wind, rain, chemicals, and the movement of ice and flowing water. The Appalachian Mountains in the eastern United States have become rounded and crumbled after millions of years of weathering by natural forces.
Erosion is a process that works with weathering to change surface features of Earth. Erosion is a process by which weathered bits of rock are moved elsewhere by water, wind, or ice. the Grand Canyon was formed by weathering and erosion caused by flowing water and blowing winds. Water flowed over the region for millions of years, weakening the surface of the rock. The moving water carried away tiny bits of rock. Weathering and erosion cause different materials to break down at different speeds. Soft, porous rocks, such as sandstone and limestone, wear away faster than dense rocks like granite.
Draw a bunny bouncing on a trampoline being chased by flying carrots.
Buildup and Movement
The buildup of materials creates landforms such as beaches, islands, and plains. Sand and other materials carried by ocean currents build up on mounds of volcanic rock in the ocean, forming islands. Entire valleys and plains can be formed by the incredible force and weight of large masses of ice and snow. A glacier, the smallest of the ice masses, moves slowly over time, sometimes spreading outward on a land surface. Ice caps are high-altitude ice masses. Ice sheets, extending more than 20,000 square miles (51,800 sq. km), are the largest ice masses. Ice sheets cover most of Greenland and Antarctica.
Human actions have changed Earth in many ways. Activities such as coal mining have leveled entire mountains Pollution caused by humans can change Earth. When people burn gasoline and other fossil fuels, toxic chemicals are released into the air. The chemicals poison waterways, kill plants and animals, and cause erosion. Studies show that humans have changed the environment of Earth faster and more broadly in the last 50 years than at any time in history.
Ch 2 Lesson 2 Conclusion
Changes to Earth’s surface caused by natural weathering and erosion happen slowly. They create different kinds of landforms that make our planet unique. Erosion and other changes caused by humans can damage Earth’s surface quickly. Their effects threaten our safety and survival. We need to protect our environment to ensure that our quality of life improves for future generations