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The Physical Earth


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The Physical Earth

The earth is the third planet from the sun -- and the only planet known to have water exist in all 3 forms.
Liquid water on earth is what makes life possible.
The availability of water has huge geographic consequences for the people living on earth.
The earth is essentially a perfect sphere -- there is a bit of variation in polar and equatorial circumferences -- caused by rotation.
Rotation causes a slight flattening of the polar regions, and a slight bulging in the equatorial zone.

Questions and Answers about the Earth's Rotation

The surface of the earth consists of water and land -- essentially, continents and oceans.
Landmasses make up approximately 30% of surface, with the remainder consisting of the vast oceans.

Test Your Knowledge of the Continents and Oceans

Continents are based on masses of granitic rock which 'float' on the denser basaltic rock beneath them and that also composes the ocean floor.
Every continent has a shield area which firmly attaches it to the crust of the earth.  These shield areas a very old rockmasses that commonly contain a wealth of metal ore minerals and add invaluably to wealth of the countries located upon them.

Today, it is known that the continents are not rigidly fixed to the crust, but rather are propelled by slow moving convection currents in the upper mantle.
It is the movement of continents that constantly produces movements of the land surface -- both up and down.   In some cases, mountains and plateaus are produced -- in others, structural lowlands.
Erosion of these surfaces produces a variety of landforms.

The Structure of the Earth Continents - Oceans - Plate Movements

Plate Tectonics -- the Story of Drifting Continents

The crust of the earth is said to be restless . . . the above links tell why.
Any place on earth is caught in the struggle between the Internal Forces of Volcanism and Diastrophism and the External Forces of Weathering and Erosion.
Internal Forces build the earth up and/or restore positive surfaces -- while the External Forces wear the surface down.
This results in what are known as Landforms.
The primary landforms on earth are:   Mountains and Hills  --  Plateaus  --  Plains  --  River Valleys  --  and Seacoasts.
These are the surfaces on which people live, with each having its advantages and disadvantages.

Photos of Various Landforms Produced by Forces of Erosion

Mountains and Hills  -- 
Mountain building activities bring rock from deep within the earth to the surface, where the mineral wealth they may contain can be found.  Mountains also force air to rise, cool, and condense, so forests in mountain areas are quite common.  Mountains also provide deep canyons for the development of hydroelectric installations, and well as beautiful scenery for the tourism industry.  Sheltered valleys within the mountains may be the site of agricultural activities.
Plateaus  -- 
Plateaus are described as a 'level surface' high above sea level.  Two general types of plateaus exist -- those between mountain ranges and those called table-top plateaus.   Plateaus tend to be cooler and drier than surrounding lowlands, and are often used for grazing livestock, or farming using special 'dry farming' methods.  Due to their height, plateaus may contain deep canyons which interfere with transportation across their surface.
Plains  -- 
Plains are level surfaces close to sea level.  The ease of transporation, fertile soils, and favorable climate of many plains makes them an ideal place for people to live.  While mountains and hills often contain metal ore minerals, plains may contain deposits of coal or oil to be used as fuel.  A great many of the world's people live within regions of plains.
River Valleys  -- 
Another favorable place for people to live is alongside a river, with its attendant fertile soil, and ready-made transportation system.  Rivers provide water, and oftentimes sources of food as well.  The great river valleys of the Far East are densely populated places.
Sea Coasts  -- 
Often seen as a more favorable place to earn a living than farther inland.  Sea coasts provide a ready source of food in many cases, and possibilities for transportation and trade.  Certain sea coasts are excellent recreational locations.

Facts About Mountains

Photos of the Colorado Plateau

Photos of Plains

Rivers and River Valleys

Articles About Physical Geography

Spectacular Erosional Landforms

Physical Earth Discussion and Links

Weather Climate Vegetation