Models and Dimensions of Earth
Study Guide
I.
Model
A. Model- is anything that represents properties of an object.
B. Types and Examples of Models:
1. Physical- provides us with information through our sense of
sight. Example: globe
2. Mechanical- a physical model with sorting parts so that it can
perform the functions or movements as the original object.
Example: model train
3. Mathematical- mathematical relationships expressed by
symbols, formulas and equations.
Example: Volume= length X width X height
4. Graphic- a graph to provide a ‘picture’ of a relationship of
symbols, formulas and equations. Example: line graph
5. Mental- models that can only exist is someone’s mind.
Example: water molecule
II.
Shape of Earth
A. Oblate Spheroid- flattened sphere.
1. Earth is flattened at the poles.
2. Earth bulges at the equator.
3. Earth’s equatorial circumference is greater than its polar
circumference.
B. Causes of Earth’s Shape
1. Gravity- This is an inward pulling force which pulls inwardly
in all directions and causes the earth to be spherical.
2. Centrifugal Force- This is an outward force caused by the
rotation (spinning) of earth on its axis which causes the earth to
bulge at the equator. The faster the rotational speed, the
greater the centrifugal force.
C. Evidence of Earth’s Shape
1. Photographs from space reveal that Earth is almost a perfect
sphere.
2. Observations of ships on the horizon indicate the gradual
‘appearance’ or ‘disappearance’ of the ship over the horizon;
this is evidence that Earth’ surface is curved.
3. Observations of an Eclipse of the moon- Earth’s shadow on
the moon (full moon) during a lunar eclipse provide evidence
that Earth is spherical.
4. Measurements of Gravity- the shorter the distance between
two objects, the greater the gravitational force. Therefore a
person or object that is closer to the center of the Earth (the
center of gravity) would weigh more than when the person or
object is farther from the center of gravity. Because Earth is an
oblate spheroid a person would be closer to the center of the
Earth at the poles and would weigh more than a person who is
at the equator.
5. Observation of the North Star, Polaris- the altitude*of
Polaris changes as an observer moves north or south (in the
Northern Hemisphere; this is because Earth is spherical and its
surface is curved. *Altitude is the height, measured in degrees
that a heavenly body (Polaris) is above the horizon of the
observer. Summary: The altitude of Polaris (above the
horizon) is equal to the latitude of the observer.
III.
Size of Earth
A. Earth’s equatorial diameter is larger than its polar diameter. (Reference
Table p. 15)
IV.
Latitude and Longitude
A. Latitude- angular distance north or south of the Equator.
1. Parallels- lines used for measuring latitude; they run East-West
‘parallel’ to the Equator.
2. Equator- 0 Latitude; this is the starting place for measuring
latitude.
3. North/South Pole- 90 Latitude; this is maximum latitude.
B. Longitude- angular distance East or West of the Prime Meridian.
1. Meridians- lines used for measuring longitude; they run
North/South from pole to pole.
2. Prime Meridian- 0 Longitude; this is the starting place for
measuring longitude.
3. International Date Line- 180 Longitude; this is maximum
longitude.
C. Coordinate System – The coordinate system used on Earth’s surface is
the latitude-longitude system with the equator and Prime Meridian as
reference lines. This system is used to help you determine the location of
a point on Earth’s surface.
D. Earth’s Time Zones
1. Earth rotates at a rate of 15 per hour.
2. Rotation provides a basis for our system of local time. As Earth
rotates half of the Earth is facing the sun and is in daylight; the
other half is in darkness and it is night.
3. Meridians of Longitude are the basis for the time zones.
4. When the sun is directly over a given meridian, it is 12 noon at
any location at or near that meridian.
5. Crossing the International Dateline- if you are going west, it is
one day later; if you are going east, it is one day earlier.
V.
Fields
A. Field- a region of space/area that has a measurable value of a given
property at every point.
B. Isolines- lines on a field map connecting all points of the same value.
C. Contour lines- isolines that show elevation.
D. Isotherms- isolines that show temperature.
E. Isobars- isolines that show pressure.
VI.
Topographic Maps
A. Topographic maps show the elevation of the land by using contour lines,
and show the natural and man-made features by using symbols.
B. Contour lines- isolines on a map connecting points of the same elevation.
C. Elevation- the distance above sea level.
D. Contour Interval- difference in elevation between two consecutive
contour lines.
E. Index Contour Line- heavy, dark contour line(s) usually with a numerical
value for elevation marked.
F. Depression Contour Line (Hachured Contour Line)- special contour
lines used to show a hole or crater on Earth’s surface. These lines are
drawn like contour lines but are marked on the inside.
G. Bench Mark (B.M.)- marker in the ground indicating the ‘exact’
elevation above sea level.
H. Spot Elevations- are the elevations of such places as road intersections,
hilltops, lake surfaces and other points of special interest. These points are
located on the map by a small cross (+), unless the location is obvious,
such as certain road intersections or hilltops.
I. Highest possible elevation of a hilltop is 1 less than the next possible
elevation or contour line.
J. The closer the lines are to each other, the steeper the slope.
K. The 3 basic features that contour lines indicate are: elevation,
steepness/gradient and shape (size).
L. River Valleys (the Law of V’s)- contour lines bend upstream where they
cross a river. This can be used to determine the direction in which a river
is flowing. The V’s point to the source of the river.
VII.
Topographic Map Skills
A. Steps to Constructing a Profile (Side View) from a Topographic Map:
1.
Draw a line between the designated points on the contour map.
2.
Place a strip of paper along the line between these points on the
contour map.
3.
Make a mark on the strip of paper wherever the paper crosses a
contour line.
4.
Label the marks with the corresponding value of the contour line
5.
Place the strip of paper along the edge of a graph or piece of lined
paper.
6.
Project the marks upward to locate the points of the profile.
7.
Draw a line connecting the points. Remember to have your line
indicate an elevation above (for a mountain or hill) or below (for a
depression) your highest contour line.
B. Gradient- rate at which elevation changes from place to place.
1. Gradient Formula (Reference Table p. 1)
VIII. Parts of Earth
A. The three ’spheres’ of outer Earth:
1. Atmosphere- the shell of gases that surrounds Earth. The
atmosphere is the least dense.
2. Hydrosphere- the waters of Earth; its oceans, seas, lakes and
rivers.
3. Lithosphere- the dense, solid outer shell of Earth composed of
rock. The lithosphere is the densest. 29% of Earth’s surface is
covered by land.
B. Earth’s Interior
1. Crust
2. Mantle
3. Inner Core
4. Outer Core
XIV. Reference Tables
A. You must be able to understand and use the following reference tables:
1.
2.
3.
4.
Formulas (Gradient)- page 1
Generalized Bedrock Geology of New York State- page 3
Inferred Properties of Earth’s Interior- page 10
Average Chemical Composition of Earth’s Crust, Hydrosphere and
Troposphere- page 11
5. Selected Properties of Earth’s Atmosphere- page 14