The Earth

© Lisa Michalek

Earth’s Shape

• Earth is an oblate spheroid, slightly flattened at the poles and bulging a little at the equator.

• From outer space, Earth looks perfectly round and smooth.

Earth’s Structure

• The Earth has three major parts:– Lithosphere (solid)– Hydrosphere (liquid)– Atmosphere (gas)

The Lithosphere

• The dense, solid shell of the earth composed of rock and soil that surrounds the more fluid inner layers.

The Hydrosphere

• The waters of the earth including the oceans, lakes, rivers, and water in the ground.

• Covers 70% of the earth’s surface.

The Atmosphere

• The shell of gasses that surround the earth and is layered into zones.– Troposphere contains the

gasses necessary for life.• 78% nitrogen, 21% oxygen,

1% other gasses.• Strong winds and storms along

with most of the water vapor and clouds .

– Stratosphere– Mesosphere– Thermosphere

Earth’s Magnetic Field

• Our planet has a magnetic field as if a giant bar magnet were buried within Earth.

• When you use a magnetic compass, the compass needle points toward Earth’s magnetic pole that is very close to the geographic north pole.

Locating Positions on Earth

• Coordinate System– Scientists have established a surface grid (lines)

that you can use to locate any position on Earth.– Each pair of coordinates (2 numbers) are called

the latitude and longitude.• Latitude are distances in degrees north or south of

the equator.– The Equator is an imaginary line that circles the Earth

halfway between the North Pole and the South Pole.

• Longitude are distances in degrees east or west of the prime meridian.

– The Prime Meridian is an imaginary line that runs through Greenwich, England, from the North Pole to the South Pole.

Coordinate System

Navigation

• The science of locating your position on Earth.

• Any location north of the equator has a latitude that is equal to the angle of Polaris (the North Star’s altitude) above the horizon.

Finding the North Star Polaris

Navigation

Finding the Altitude of a Star

• The altitude is the angular height above the horizon.

• Measurement can be made using an astrolabe.– A protractor with

a heavy weight suspended.

Solar Time and Clock Time

• Clock time is based on observations of the sun.

• Noon is the time when the sun reaches its highest point in the sky.

Calculating Longitude

1. Find the difference between local clock time and Greenwich time.

2. Multiply this time difference by 15° per hour.

3. If local time is earlier than Greenwich time, your position is West of the prime meridian or West Longitude.

4. If local time is later than Greenwich time, your position is east of the prime meridian or East Longitude.

Fields

• A region of space where every point or location can be measured.

• Isolines connect points of equal values on a field map.

• Isotherms connect points of equal temperatures.

• Isobars connect points of equal air pressure.

• Contour lines connect point of equal elevation.

Field Maps

This map has all of the isolines drawn in, at an interval of 10 (each line is 10 units apart)

The numbers on the map represent the concentration of gasoline found at that location. So the map simply shows how much of something (in this case gasoline) is found at many locations.

Topographic Map (Contour Map)

• Show the shape of the Earth’s Surface.

• Contour lines drawn on a map give the elevations for a region.

• Where the lines are close, the slope of the ground is steep.

• Where the lines are far apart, the slope of the ground is gentle.

Contour Map Example

1. Which hill is higher, hill A or hill B?

2. Which hill is steeper, hill A or hill B?

3. How many feet of elevation are there between contour lines?

4. How high is hill A? Hill B?

5. Are the contour lines closer on hill A or hill B?

On this map, the vertical distance between each of the contour lines is 10 feet.

Topographic Profile

• A cross sectional view that shows the elevation of the land.

Determining Gradient and Slope

• The rate of change in field values between two points in a field.

• The average slope, or gradient, between any two points (A and B) on a mountain can be determined from a contour map.

Distance between A and BGradient =

Difference between A and B

Determining Gradient Sample Problem

• Calculate the average slope of a mountain trail from the 980-meter contour line to the 480-meter contour.

• The distance between these two elevations measures 4 kilometers.

Distance between the points (km)Gradient =

Difference in elevation (m)

= 980 m – 480 m 4 km

= 500 m 4 km

= 125 m/km