Ch. 2-2 The Land

To understand volcanoes and earthquakes, you must first know… The Earth is about 70% water (like your body) and only 30% land. Continents are special because of their landforms, or shapes and types of land.

Common landforms Mountains… usually rise more than 2,000 feet above sea level are wide at the bottom and rise steeply to a narrow peak at the top.

Common landforms Hills… are lower than mountains and less steep with rounded tops.

Common landforms Plateaus… are large, mostly flat areas that rise high above the land and are steep on at least one side.

Common landforms Plains… are large areas of flat or gently rolling land.

Clues to the earth’s history Geographers began to notice patterns in the landforms. They found similarities in landforms that are on different continents and are very far away. This lead geographers to a new theory…

Pangaea, the supercontinent Geographers theorize that millions of years ago all land on Earth was connected and was one huge landmass…

Pangaea, the supercontinent …and that over millions of years, Pangaea split into several pieces, eventually forming separate continents.

But… WHY did the continents separate?

plate tectonics says the outer skin of the Earth, called the crust, is broken into huge plates.

The continental plates are on the top layer of the crust Continents and oceans are the top of the crust. The plates float on a layer of hot magma (the same stuff that flows from volcanoes). The plates move and shift over time, altering our Earth’s surface.

Continental plates move

Plates can come together in one of three ways, changing the surface of the Earth, and changing landforms:

2. 3. 1. Continental plates push into each other and one plate is forced under the other. There is LOTS of pressure and volcanoes form. Continental plates move alongside each other and the crust cracks, called faults, and causes earthquakes. Continental plates move apart and hot magma leaks up. In oceans, this forms underwater mountains called ridges.

2. 3. 1.

Breaking the earth down Forces like volcanoes build the Earth up, creating new landforms. Other forces break it down. weathering This is called

Weathering Rain, ice, air pollution, and tree roots wear away at the Earth’s landforms, breaks down landforms, and creates tiny pieces of rock, which can create new soil.

Erosion Small pieces of rock are moved (by rain, water, or wind), called erosion …thus creating new landforms.