The Physical Earth

M&R Geography-Geology

The Physical Earth

On this page, we will look at the physical earth -- the structure and processes that shape our planet.

The earth is part of the solar system -- the 3rd planet from the sun.

The earth is a dynamic planet -- constantly changing in both violent and subtle ways.

Geologists have measured the age of the earth at 4.6 billion years from the time it became solid -- possibly as old as 10 billion going back to its formative stages.

The surface consists of continents and oceans -- around 30% land, 70% water.

It is of course the land where people live -- and it it from this perspective that a knowledge of the land surface and what it means to people becomes important.

First, a look at the general structure of the earth:

Motion of material inside the earth produce dramatic changes on the surface. These include volcanism and movements of the solid crust (diastrophism).

The events produce positive relief forms of the continents and other masses of land.

These Internal Forces produce features on the land surface called 'Landforms' -- the branch of Geology that studies this subject is called Geomorphology.

For many years the forces behind this restlessness of the crust were not known. Today, the Theory of Continental Drift and its complementary Theory of Seafloor Spreading give us the answers.

Together these theories are called Plate Tectonics.

Another set of forces act to modify the surface produced.

These are the External Forces -- Weathering and Erosion.

Weathering is a complex of processes that disintegrate rock into smaller pieces or new materials. Weathering is two general processes called Physical Weathering -- reducing rock particle size; and, Chemical Weathering which changes the rock's compostion into simpler (chemically) earth materials.

Through the action of the plates, colliding, pulling apart, or sliding past each other the major landforms of the earth are produced.

The major landforms are Mountains, Hills, Plateaus, and Plains -- and it is upon these surfaces that people must live. Each has it advantages and disadvantages.

Mountains -- Bring ancient rock to the surface in many cases, where

metal ore minerals may be found.

Due to the orographic effect, mountains are often

Beautiful scenery provides recreational opportunities.

Rivers and canyons provide sites for hydroelectric

Hills -- Hills may be as steep as mountains, but the slopes are

Hills may have many of the geographic resources as

Plateaus -- Plateaus are relatively level surfaces high above sea

Oftentimes somewhat drier than surrounding areas

land use is limited to livestock production and dry

Deep canyons cut through plateaus disrupt

transportation, but do afford places for dams and

hydroelectric development.

Plains -- Plains are relatively level areas close to sea level.

Advantages often include fertile soil for farming, ease of

transportation, and availability of fuels -- coal, oil, and

Most of the world's people live in areas of plains.

Forces of erosion immediately begin to affect any newly produced landform -- all landforms are constantly in the process of being built on the one hand and being destroyed on the other. At any time and place one of the forces -- constructive or destructive -- may be the dominant factor.

The major forces of erosion are Running Water, Wind, and Glacial Ice.

As the forces of erosion attack the rock structure, various relief forms are produced according to the pattern of rock being weathered and eroded.


				*M&R Geography-Geology* *The Physical Earth*



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