Earth’s Landmasses

Earth’s Landmasses There are only four major landmasses on Earth. A continent is a landmass that measures millions

of square kilometers and rises a considerable distance above sea level.

Each continent has at least one large area of very old rock exposed at its surface called the shield.

Shields form the cores of the continents.

The Continents There are seven continents: Asia Africa Australia North America South America Antarctica

Earth The largest landmass on Earth consists of three

continents – Asia, Africa and Europe. The second largest landmass consists of the

continents of North America and South America. The third largest landmass is Antarctica. It is

about twice the size of the United States. The smallest landmass is Australia.

Antarctica Antarctica is very different from the other

continents. It is almost completely covered by a thick icecap

which covers 34 million square kilometers. It contains 90% of the ice on Earth.

It is the coldest area on Earth. In 1983, Volstok dropped to nearly –89.2 degrees C.

Many scientific stations have been built here.

Australia Australia is the smallest landmass still considered

a continent. It is the only continent that is a single country.

Changes in the Earth’s Surface Over billions of years, the surface of the Earth has

changed many times. Several factors produce these changes; Weather conditions such as heat and wind change

the surface. Running water reshapes the land. Earthquakes and volcanoes cause major changes. People also alter the Earth’s appearance.

Topography Scientists refer to the shape of the Earth’s surface

as its topography. The Earth’s topography is made up of different

kinds of landscapes. A landscape is the physical features of the Earth’s

surface found in an area.

Landscapes There are three main types of landscape regions:

mountains, plains and plateaus. One characteristic of a landscape region is

elevation, or height above sea level. The difference is a region’s elevation is called its

relief. If a landscape has high relief, there are large differences in the elevations of different areas within the landscape region.

Mountains Mountains make up one type of landscape region.

Mountains are natural landforms that reach high elevations.

Mountains have narrow summits, or tops, and steeps slopes, or sides.

A mountain must rise at least 600 meters above the surrounding land.

Highest Mountains The highest mountain in the world is Mount

Everest, ( 8 km) a part of the Himalayas. The Himalayas extend from Tibet to Pakistan. The highest mountain in the United States is

Mount McKinley (6 km) in Alaska.

Mountains Age All mountains did not form at the same time. Some mountains are very old, some young.

Mountains are built very slowly. The Rocky Mountains began to form about 65 millions years ago. It took 10 million years for them to reach their maximum height. Geologists consider the Rockies to be “young”.

Mountain Formation Mountains can be formed in several ways. Some mountains result from the folding and

breaking of the Earth’s surface. Other mountains are created when hot magma

(liquid rock) from the Earth’s interior breaks through the Earth’s surface.

Streams and Rivers Streams and rivers in mountain areas move very

quickly. The higher and steeper the mountain slopes, the faster the water flows.

Mountains rivers and streams carry rocks of all sizes. Streams and rivers often carve valleys in mountains. Valleys in older mountains are wider.

Individual Mountains Individual mountains, which are not part of a

group, can be found in parts of the world. They are usually the products of volcanic activity during which magma broke through the Earth’s surface.

Examples of volcanic mountains are Fujiyama in Japan, Vesuvius in Italy and Kilimanjaro in Tanzania.

Mountain Range Most mountains are part of a group called a

mountain range. A mountain range is a parallel series of mountains that have the same general shape and structure.

A group of mountains ranges in one area is called a mountain system. The Great Smoky, Blue Ridge, Cumberland, and Green mountain ranges are all in the Appalachian mountain system.

Mountain Belts Most mountain ranges and systems are part of an

even larger group of mountains called a mountain belt.

There are two major mountain belts in the world. The Circum-Pacific belt rings the Pacific Ocean. The Eurasian-Melanesian belt runs across northern

Africa, southern Europe and Asia. The two belts meet in Indonesia.

Plains Another type of landscape region is made up of

plains. Plains are flat land areas that do not rise far above

sea level. Plains have very small differences in elevation. They are areas of low relief. The difference in elevation in a plains may be less than 100 meters.

Most plains have broad rivers and streams.

Coastal Plains A coast is a place where the land meets the ocean.

Low, flat areas along the coasts are called coastal plains. The Atlantic and Gulf coastal plains are examples. The coastal plains of the United States were formed when soil and silt were deposited on the edge of the continent. In the past, shallow oceans covered these areas. The oceans disappeared and sand and silt were left behind creating fertile farming land.

Interior Plains Some low, flat areas are also found inland on a

continent. These areas are called interior plains. Interior plains are higher above sea level (450m) than coastal plains. The Great Plains are large interior plains. They were formed as mountains and hills that were later worn down by wind, streams and glaciers. Interior plains have good soil since sediments have been deposited by rivers and streams.

Plateaus A third type of landscape region consists of

plateaus. Plateaus are broad, flat areas of land that rise more than 600 meters above sea level. Some plateaus reach elevations of more than 1500 meters. Plateaus are not considered mountains because their surfaces are fairly flat. Like plains they have low relief, but unlike plains they rise much higher above sea level.

Location of Plateaus Most plateaus are located inland but a few are near

oceans. The plateaus near oceans often end in a cliff at the edge of a coastal plain or in a cliff at the coast.Plateaus have the same landscape for thousands of kilometers. Some plateaus have been deeply cut be rivers and streams that form canyons. The Colorado River cuts through the Colorado Plateau to form the Grand Canyon in Arizona. Most are dry and used for grazing or mining.

Mapping the Earth’s Surface A map is a drawing of the Earth, or a part of the

Earth, on a flat surface. The most accurate representation of the entire

surface of the Earth is a globe, a spherical model. Both maps and globes are drawn to scale. A scale

compares distance on a map or globe to actual distances on the Earth’s surface.

Meridians Each meridian is half of an imaginary circle

around the Earth. Geographers have named the meridian that runs through Greenwich, England, the prime meridian.

Because meridians run north and south, they measure distance east and west. The measure of distance east and west of the prime meridian is called longitude.

Distance The distance around any circle, including Earth, is

measured in degrees. All circles contain 360 degrees.Each meridian

marks 1 degree of longitude around the Earth. The prime meridian is labeled 0 degrees longitude. Meridians to the west are called west meridian and

to the east, east meridians. They go from 0 to 180.

Time ZonesIn one day the Earth rotates 360 degrees or 15

degrees every hour. Thus, the Earth has been divided into 24 zones of 15 degrees longitude each. These zones are called time zones.The Earth rotates on its axis from west to east so the sun appears to rise in the east and travel west. Time zones become an hour earlier in each zone.

Time Zones There are four time zones in the contiguous United

States. From east to west they are: the Eastern, Central, Mountain, and Pacific time zones. Hawaii and Alaska are further west than the Pacific time zone.

International Date Line The international date line is located along the

180th meridian. When you cross this line going east, you subtract one day.

When you cross this line going west, you add one day.

Parallels There are also lines from east to west across a map

or globe. These lines are called parallels. Parallels cross meridians at right angles.

The parallel located halfway between the North and the South poles is the equator.

Because parallels run east and west, they measure distance north and south which is known as latitude.

Equator The equator is labeled 0 degrees latitude. Parallels to the north of the equator are north

latitudes. Parallels to the south of the equator are south

latitudes. The distance from the equator to either the North or South pole is one quarter of the distance around the Earth. North and south parallels are labeled from 0 to 90.

Types of Maps Maps show locations and distances on the Earth’s

surface. They also show many different local features. Some maps show soil types in an area. Some show currents in the ocean. Some show small, detailed areas of the Earth.

Drawback of Maps Maps have one serious drawback. Because they

are flat, maps cannot represent a round surface accurately.

A map is a projection or representation of a three-dimensional object on a flat surface. When the round surface of the Earth is represented on a flat surface, it is distorted.

Mercator Projections There are many different ways to project the

Earth’s image onto a map. One type of map projection is Mercator projection. They are used for navigation. They show the correct shape of the coastlines. The sizes of land and water areas become distorted in latitudes far from the equator.

Equal-Area Projections Another type of map projection is called an equal-

area projection. Equal-area projections show area correctly. The meridians and parallels are placed on the map is such a way that every part of the Earth is the same size on the map as it is on a globe but the shapes of the areas are distorted on an equal-area projection.

Topographic Maps A map that shows the different shapes and sizes of

a land surface is called a topographic map. This type of map may also show cities, roads, parks and railroads.

Topographic maps show the relief of the land.

Contours Most topographic maps use contour lines to show

relief. A contour line is a line that passes through all points on a map that have the same elevation.

The difference in elevation from one contour line to the next is called the contour interval. For example, in a map with a contour interval of 5 meters, contour lines are drawn only at elevations of 0 meters, 5 meters, 10 meters and 15 meters.

Symbols Topographic maps use symbols to represent

features. Symbols for buildings and roads are usually black.

Symbols for bodies of water such as rivers, lakes and streams are blue.Green represents woods and swamps.Contour lines are brown or red.

All symbols are placed in a legend which explains what each symbol represent.

Rules of Topographic Maps A contour line of one elevation never crosses a line of

another elevation. Closely spaced contour lines represent a steep slope since

the elevation changes greatly over a short distance. Contour lines that cross a valley are V-shaped. If a stream

flows through, the V will point upstream. Contour lines form closed loops around hilltops or

depressions. Hachures are also used to indicate a depression.