Forces Shaping the Earth Unit 2, Section 2

Earthquakes and volcanoes are two forces that shape and reshape the Earth. About 80% of the world’s earthquakes and many of the active volcanoes occur along the ‘Ring of Fire’.

Crust: only 8-40 kms thick, layer of rocks and minerals that floats on top of the mantle. Mantle: about 2900 kms thick, it is a hot, rocky layer that surrounds the core. Outer Core: mostly molten, or liquefied metal. Inner Core: solid because of the great pressure of the mantle and crust around it. (together the inner and outer core are 3500 kms thick.

Water on Earth Saltwater Areas 97% of Earth’s water is saltwater found in the Oceans. (Atlantic, Pacific, Indian, and Arctic) Most gulfs, seas, and bays are areas of saltwater partially enclosed by land. A strait is a narrow channel of water that connects 2 larger bodies of water.

Water on Earth Freshwater areas Only make up 3% of Earth’s water supply. Most freshwater is locked in ice sheets around the North and South Poles. Other freshwater is found in lakes, streams, and rivers. A lake is a body of freshwater surrounded by land.

Water makes up 70% of the Earth’s surface and Land only makes up 30% The largest landmasses on Earth are the 7 continents – Europe, Asia, Africa, North America, South America, Australia, and Antarctica.

Above Earth’s surface is the atmosphere, a layer of gases a few miles thick. It provides oxygen to people and animals, and carbon dioxide to plants

Land Forms The Earth’s surface is made up of many different landforms. The 4 major landforms are– mountains, hills, plains and plateaus. These landforms differ in shape and elevation – the height of land above sea level.

Land Forms Mountains are high, rugged landforms with a narrow peak or ridge. A mountain rises more than 2000 feet above sea level. Hills are raised areas of land that are lower and less steep than mountains and have more rounded tops.

Land Forms A plain is a large area with either level or rolling land. Plains may be located along a coast, or inland. A plateau is like a plain, but is located at higher elevations than a plain. It may also have 1 or more steeply dropping edges.

The Changing Earth: Forces From Within Rising magma from beneath the Earth’s surface forms new crust along seams between Earth’s plates. Volcanoes spew molten rock, or lava from inside the Earth.

Many scientists think that about 200 million years ago the continents were joined together in one supercontinent called Pangaea. Matching rock types, and matching fossils have been found in both Africa and South America. This helps prove this theory. Also scientists have found evidence that the sea floor is spreading apart. Pangaea Game

The Earth’s crust floats on the other layers The Earth’s crust floats on the other layers. It moves but not all in one piece, but in sections. These sections are called plates. This movement takes place very slowly (2-5 cm a year)

Mountain Building Folding: when two sections of Earth’s crust push together, the crust may fold, or buckle in wavelike patterns. (Rocky Mountains) Fault: is a crack in a tectonic plate caused by built up pressure between two colliding plates. (Sierra Nevada Mountains) Volcanic Action: takes place when plate movement causes magma (melted rock) to escape from the mantle through the earth’s crust. Usually a cone shaped mountain is left. (Mauna Kea)

Forces From Without Water, ice, wind all help to change the face of the Earth. Weathering: is a process that breaks rocks down into tiny pieces. Weathering helps to create soil. Erosion: is the removal of small pieces of rock by water, ice, or wind.

The Appalachian Mountains were as high as the Rocky Mountains now are. Rain, snow, and wind slowly wore them down into much lower peaks.

When water, ice, and wind remove material, they deposit it downstream or downwind to create new landforms. Plains and deltas are often made of material carried downstream by rivers.