Unit One Dimensions of the Earth

In this unit we will discuss the size and shape of the Earth and how these measurements were obtained. Locating and mapping positions on Earth will
also be discussed (i. e., latitude and longitude).

I. How Can the Earth's Shape be Determined?
A) Nature of the Earth's Shape and Surface
1) Earth's shape is an oblate spheroid -slightly flattened at the poles and slightly bulging at the equator

a) Equatorial Diameter = 12,756 km
b) Polar Diameter = 12,714 km
2) Oblateness caused by Earth's rotation
3) Earth is very smooth in comparison to its diameter -we will do a lab on this!

B) Evidence of the Earth's Shape
1) Shadow of Earth during lunar eclipse is round
2) Ships disappeared bow first over the horizon
3) People viewed the Sun setting later from mountains than from sea level.
4) Polaris (North Star) "moves" in the sky when a person travels north or south. This is always equal to ones latitude in the northern
hemisphere.
5) Photographs from space which are very precise and are the only direct proof of Earth's shape 1
6) Gravity measurements -force of gravity is less at equator than at poles due to differences in distance to center of Earth

II. How Can the Earth's Size be Determined?
A) Eratosthenes in 235 B. C. used simple geometry and the fact that the Earth is 360 degrees in circumference.

III. The Layers of the Earth
A) The Lithosphere -solid outer layer of soil and rock extending form the surface to a depth of about 100 km.

B) The Hydrosphere -all the water on the Earth (oceans, rivers, lakes etc.)
C) The Atmosphere -all the gasses that surround the Earth due to gravity. It contains mostly nitrogen and oxygen.

See Earth Science Reference tables and graphs.
D) The Positions of the Earth Layers
1) The Earth layers arrange themselves according to their density. The top layer, the atmosphere, is most dense and the bottom layer, the
lithosphere, is least dense.
2) See Earth Science Reference Tables for tables and graphs.

III. How can the Earth's Surface Features be Mapped?

Maps are models of the Earth that are usually drawn on a two dimensional surface. Globes are the most accurate because they are the same shape as the
Earth.
A) Latitude and Longitude
1) Latitude -measures distance north or south of the equator.
a) These lines are sometimes called parallels -they never intersect
b) Important Latitude Numbers:
Equator = 0 degrees lat., separates Earth into north and south hemispheres

North Pole = 90 degrees North, South Pole = 90 degrees South
2) Longitude -measures east or west of the prime meridian
a) These lines all intersect and form points (or poles) at the north and south poles.

b) Important Longitude Numbers:
Prime Meridian = 0 degrees long., separates the Earth into east and west hemispheres

International Dateline = 180 degrees long.
c) Time Zones -each 15 degrees of long. = a one hour time change or time zone

360 degrees of circumference/ 24 hours per day = 15 degrees of long./ hour
B) Field Maps -these maps try to show the Earth in 3 dimensions with the use of isolines.
1) Isolines -connect points of equal value (temp. and elevation are examples)
2) Gradients -the rate at which field values change
Gradient = Amount of change in field value/ Distance through which change occurs

We will be having a lab this!
3) Fields are usually changing over time; they rarely remain the same
C) Topographic Maps These are types of field maps that depict the Earth in 3 dimensions on a two dimensional surface with the use of contour lines.
Contour Lines -connect points of equal elevation (a type of field line)
Contour Interval -the difference in elevation between two contour lines next to each other. Listed on a topographic map.

Reading Contour Maps: Contour lines never cross; they form circles around hills; they form a V at rivers that point up stream.
1) Symbols -these are provided for in topographic maps
2) Map Scale -converts maps distance into actual distance. Found on all maps.

3) Map Direction -top is north. There is a difference between geographic and magnetic north called magnetic declination.
4) Map Profiles -this is a cross section of what the land would look like between two points
We will be having a lab on topographic maps and map profiles to explain these concepts further