5. Earth's Interior
Expedition Menu
To understand the theory of
plate tectonics,
let's first begin by examining a "pie-shaped"
slice into the interior of the Earth.
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Here we see the principal rock layers within the Earth, which have been identified through a combination of earthquake wave analyses and laboratory experiments using rock samples at high pressures and temperatures.
First note that the diagram above is NOT to scale, but a highly exaggerated cartoon.
Second, notice the distances to the boundaries between the layers and the distance to the center of the Earth -- these are in kilometers or the abbreviation "km"
On your handout draw a picture of the Earth model shown above and label the layers and the distances in both kilometers and miles (you will need to calculate the distances in miles using
1 kilometer = 0.6 miles
Note the principal layers are labeled along the left side of the diagram -- beginning at the center of the Earth with the core, mantle and crust:
Core (in gray) consisting of both a solid inner core and a liquid outer core. The core, both inner and outer parts, is composed mainly of iron (chemical symbol "Fe"). The interior of the earth is very HOT -- several thousands of degrees (centigrade).
The very hot temperatures within the interior of the earth produce motions of the liquid iron in the outer core (currents), much like the motions of boiling water (although much slower).
Motion of material that is driven by heat is called convection.
- The Mantle Layer (in yellow, two shades of orange and light beige), between the core and the crust, composes the greatest volume of the Earth. The mantle is composed of rocks with large amounts on magnesium (chemical symbol "Mg") and iron (Fe) with some silicon (chemical symbol "Si") and oxygen (chemical symbol "O") -- the rocks in the uppermost part of the mantle (light beige) are solid, whereas rocks in the middle portion of the mantle (deep orange region) are weak -- the high temperatures given off by the liquid outer core, cause the rocks to be weak. allowing them to flow albeit very slowly.
- So we have a second region
of movement of weak, soft rocks in portions of the upper
mantle that once again flows by convection.
- Finally there is the crust (in brown) on the surface of the Earth. This is the rocky layer on which you are currently standing (sitting?). We will later learn more about the crust, in particular that the crust under the ocean is very different from that composes the continents.
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On your handout make a line scale - like a ruler - down the left column of the page -- at least 6.5 inches long. At the top of the scale mark a "0 (zero=surface)" - at the bottom write "6370 km (center of Earth)" -- divide the scale into 13 equally spaced divisions -- each 1/2 inch long and representing a distance (depth) of 500 kilometers.
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Remember that 500 kilometers is 300 miles
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Make tick marks on your ruler at the exact places of each boundary between the layers (i.e. boundary between the crust and mantle, between the mantle and outer core, and between the inner and outer core)
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From a previous expedition -- remember the average water depth of the seafloor? This is the average thickness of the ocean layer -- try to draw the ocean layer on your line scale -- can you do it?
Created By:
Don Reed
Dept. of Geology
San Jose State University
©Copyright 2008
Last Updated on
Sept. 22, 2008
Based on your diagrams and the line scale, the oceans compose:
a) the majority of our planet,
b) much of the our planet,
c) a very, very thin layer spread out over the surface of our planet