Earth image Earth's Surface Features

Dr. Pamela Gore
Georgia Perimeter College

Objectives

  1. Describe the major features of the Earth, including size, shape
  2. Describe the major features of the Earth's surface including continents, oceans, and linear mountain belts.
  3. State the lowest (or deepest) point on Earth, the highest point on Earth (in terms of elevation), and the tallest mountain (distance from bottom to top).
  4. Discuss how plate tectonics controls topography (mountains, deep sea trenches, mid-ocean ridges, continental rifts, and faults like the San Andreas Fault).
  5. Relate plate tectonic movements to earthquakes, volcanic activity, formation of mountain ranges, and major topographic features.
This section addresses, in whole or in part, the following Georgia GPS standard(s):
  • S6E1c. Compare and contrast the planets in terms of size relative to Earth, surface and atmospheric features, relative distance from the sun, ability to support life
  • S6E3a. Explain that a large portion of the Earth's surface is water, consisting of oceans, rivers, lakes, underground water and ice
  • S6E3b. Describe the composition, location, and subsurface topography of the world's oceans

This section addresses, in whole or in part, the following Benchmarks for Scientific Literacy:
  • We live on a relatively small planet, the third from the sun in the only system of planets definitely known to exist (although other, similar systems may be discovered in the universe).
  • The earth is mostly rock. Three-fourths of its surface is covered by a relatively thin layer of water (some of it frozen), and the entire planet is surrounded by a relatively thin blanket of air. It is the only body in the solar system that appears able to support life. The other planets have compositions and conditions very different from the earth's.
  • The interior of the earth is hot. Heat flow and movement of material within the earth cause earthquakes and volcanic eruptions and create mountains and ocean basins. Gas and dust from large volcanoes can change the atmosphere.
  • The solid crust of the earth-including both the continents and the ocean basins-consists of separate plates that ride on a denser, hot, gradually deformable layer of the earth. The crust sections move very slowly, pressing against one another in some places, pulling apart in other places. Ocean-floor plates may slide under continental plates, sinking deep into the earth. The surface layers of these plates may fold, forming mountain ranges.

This section addresses, in whole or in part, the following National Science Education Standards:
  • Lithospheric plates on the scales of continents and oceans constantly move at rates of centimeters per year in response to movements in the mantle. Major geological events, such as earthquakes, volcanic eruptions, and mountain building, result from these plate motions.[
  • Land forms are the result of a combination of constructive and destructive forces. Constructive forces include crustal deformation, volcanic eruption, and deposition of sediment, while destructive forces include weathering and erosion.
  • The earth processes we see today, including erosion, movement of lithospheric plates, and changes in atmospheric composition, are similar to those that occurred in the past. earth history is also influenced by occasional catastrophes, such as the impact of an asteroid or comet.

Overview of the Earth

Size and Shape of the Earth

Size of Earth:
   Radius = 6378 km
   Diameter = 12,756 km

Compared with some of the other planets (Jupiter, Saturn, Uranus and Neptune), the Earth is fairly small.

The Earth appears to be spherical, when viewed from outer space, but the Earth is not a perfect sphere. Because of its rotation, its shape is slightly distorted. The shape of the Earth is best described as an oblate spheroid. This means that it is like a sphere, but it bulges at the middle, along the equator.

The diameter of the Earth, from pole to pole, is approximately 12,714 km.
The diameter around the equator is slightly larger, at approximately 12,756 km.
This is not a big difference, but the Earth is not a perfect sphere.

The circumference of the Earth was measured by Eratosthenes, a Greek mathemetician, geographer and astronomer who lived 276 - 195 BC. He knew that at noon on the summer solstice in Syene (in southern Egypt), the sun shone directly down a deep vertical well, illuminating the bottom. Eratosthenes recognized that the sun must be directly overhead at Syene on the summer solstice. In Alexandria, Egypt, north of Syene, he saw that the sun was not overhead directly at that time because a vertical post cast a shadow to the side. Eratosthenes measured the angle of the shadow (7.2), and knowing the distance from Alexandria to Syene (5000 stadia), he calculated the circumference of the Earth. He knew from geometry (if the Earth were a sphere) that the angle he measured was equal to the angle between Alexandria and Syene, as measured from the Earth's center. Because the arc of the angle he measured was 1/50 of a circle, he multiplied 5000 stadia by 50. His result, 250,000 stadia (or about 46,250 km), is surprisingly close to modern measurements of the circumference of the Earth (about 40,024 km). His calculation was based on two assumptions - that the Earth is a sphere and that the sun's rays are essentially parallel.

You can do this calculation for yourself, or have your students do it.
12,756 km = diameter of Earth, so divide by 2 to get the radius, r. r=6378 km.
Now use the formula for the circumference of a circle. Circumference = 2πr.
Pi (or π) = 3.1415927...
Plug in your radius and solve for the circumference of the Earth.

Distance from the sun:
The Earth is 149,598,000 km or 92,956,000 mi from Sun. (This number is commonly rounded to 93 million miles.)
93 million miles (93,000,000 mi) can be expressed in scientific notation as 9.3 x 107 mi (which you would read as 9.3 times 10 to the 7th power, miles).
The distance from the Earth to the Sun is defined as 1 Astronomical Unit (1.00 AU).
The distances of each of the planets from the sun can be expressed in Astronomical Units, or their distance relative to the distance of the Earth from the Sun.

Earth's Surface Features

A large part of the Earth is covered by water (approximately 71%). This leaves 29% of the Earth's surface as dry land.
If we were to drain out all of the water, we would see that continents cover about 40% of the Earth's surface, and ocean basins cover about 60% of the Earth's surface. (See map below).
What is the diffference?

As we can see in the image of the surface of the Earth from the National Oceanic and Atmospheric Administration (NOAA), generated from land and sea-floor elevations, the edges of the continents (continental shelves) are covered by shallow water (light blue). Other water covers parts of the continents in the form of lakes and rivers (or glacial ice).

Keep in mind that sea level changes through time as global temperatures change, and the glaciers and polar ice caps fluctuate.
So the amount of flooding of the continental shelves changes over time. During the Ice Ages, much of the Earth's water was tied up in glaciers, so sea level was much lower. In some places, almost the entire continental shelf was exposed as dry land.

Earth's surface features map
Map of Earth's Surface Features from NOAA. Click to enlarge.
This map shows what it would look like if all of the water was draine dout of the oceans.

Continents cover 40% of Earth's surface
Average elevation of continents = 840 m above sea level; 2750 ft above sea level
For comparison, the elevation of Atlanta is 1000 ft; the elevation of Dalton, GA is about 750 ft
Seven continents (in alphabetical order):
  1. Africa
  2. Antarctica
  3. Asia
  4. Australia
  5. Europe
  6. North America
  7. South America

Ocean basins cover 60% of Earth's surface
Average depth = 3800 m below SL; 12,500 ft below SL
Elevations are largely a reflection of the densities of the rock that makes up the continents or the ocean floor.
The continents are dominated by granite.
The ocean floor is dominated by basalt.
Basalt is more dense than granite, so the oceanic crust "sags" lower as it "floats" on the underlying part of the Earth that flows, called the asthenosphere (a part of the Earth's mantle).

The oceans are:
  1. Pacific Ocean (largest and deepest)
  2. Atlantic Ocean
  3. Indian Ocean
  4. Arctic Ocean
Most prominent features of continents are linear mountain belts
Circum-Pacific Belt
Alpine-Himalaya Belt

Highest point on Earth?
Mt. Everest (Himalayas) 8848 m or 29,028 ft

Most prominent features of oceans are ocean ridge systems.
Continuous belt 73,600 km or 46,000 mi long
The oceanic ridge system is the longest mountain range on Earth.

Lowest point on Earth?
Mariana Trench -11,033 m or -36,198 ft
Deep sea trenches are subduction zones (see plate tectonics section).

Tallest (not highest) mountain?
Mauna Loa, Hawaiian volcano
Base at -5000 m or -16,400 ft
Top at 4170 m or 13,677 ft
Height = 9170 m or 30,077 ft
Age nearly 1,000,000 years
30,077 ft/1,000,000 years = .03 ft/yr


What are the controls on topography?

Land forms are the result of a combination of constructive and destructive forces.

Constructive forces include crustal deformation, volcanic eruption, and deposition of sediment, whereas destructive forces include weathering and erosion. Crustal deformation and volcanic eruption are the result of plate tectonics. Weathering breaks rocks down into sand and clay and other sediment particles. Erosion is the transport of those particles from one place to another. Erosion can carve out valleys and canyons. Deposition of sedimentary particles can form deltas, dunes, glacial landforms, and many other features.

Plate tectonics controls the large-scale features of the Earth's surface, including locations of continents and oceans, locations of mountain ranges and deep sea trenches, and many other features.

Theory of Plate Tectonics
Lithosphere (Earth's rocky outer part) is divided into plates
The plates move relative to one another. The motion of the plates is due to convection (heat transfer) within the Earth.

  1. Convergent plate motion (compressional stress)
    Convergent motion means that the plates are moving toward one another.
    Convergent plate boundaries are likely to be:
    continental collisions (C-C) = mountains
    subduction zones (O-O or O-C) = deep sea trenches

  2. Divergent plate motion (tensional stress)
    Divergent motion means that the plate are moving apart from one another.
    Divergent plate boundaries are likely to be:
    Oceanic ridge spreading centers (O-O) = mid-ocean ridges
    Continental rifts (C-C) = East African rift zone, Red Sea

  3. Transform (shear stress)
    Transform motion occurs where a plate slides beside another plate.
    Transform plate boundaries are likely to be: Transform faults - most of which cut across the mid-ocean ridge.
    The San Andreas Fault is also a transform fault.

Plate movement generates earthquakes, volcanic activity, mountain ranges and major topographic features.

Seafloor spreading rates are about 5 cm/yr or 2"/yr (about the same as the rate of your fingernail growth).


Map showing the locations of the Earth's tectonic plates. Courtesy U. S. Geological Survey.


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Page created by Pamela J.W. Gore
Georgia Perimeter College,
Clarkston, GA

Page created February 16, 2005;
Modified March 12, 2005
Modified July 5, 2007
Updated May 16,2008
Updated June 10, 2009