1. Chapter 2 Measuring Earth
Earth Science
Chapter 2
Measuring Earth

2. Shape of Earth Evidence the Earth is spherical:
Photographs from space
Setting sunlight lingers on treetops, then hilltops, then clouds
Large objects appear/disappear over horizon
Eclipses
True shape of Earth is an oblate spheroid
(Flattened at poles - bulging at equator)

3. Size of Earth Earth’s structure Earth is divided into several layers
Crust = 10 km thick in oceans and
65 km beneath continents
Mantle = 2850 km thick
Outer core = 2100 km thick
Inner core = 1400 km thick (radius)

4. Size of Earth

5. Size of Earth Lithosphere Hydrosphere Atmosphere
Continuous shell of rock around Earth
Mostly covered by soil and loose rock
Hydrosphere
Thin layer of water resting on the lithosphere
Covers about 70% of Earth’s surface
Atmosphere
Thin shell of gases held to Earth by gravity
Has layers and thins out as distance from Earth increases

6. Size of Earth

7. Determining Positions on Earth
Coordinate systems
Any system for assigning two numbers to every point on a surface
The system used on Earth’s is the latitude-longitude system with the equator and prime meridian as reference lines.
When writing coordinates, distance along the horizontal line (latitude) is first, followed by distance along vertical line (longitude).

8. Determining Positions on Earth
Latitude
Angular distance in degrees, north or south of equator
Lines of latitude run east-west and are called parallels.
Equator = 0 o latitude
North Pole = 90 oN latitude
South Pole = 90 oS latitude
Observer’s latitude in Northern Hemisphere is equal to altitude of Polaris (North Star).

9. Determining Positions on Earth
Measuring Latitude

10. Determining Positions on Earth
Longitude
Measurement of the angular distance east or west of the Prime Meridian
Lines of longitude run north-south and are called meridians.
Prime Meridian = 0 o longitude
International Date Line = 180 o longitude
All other readings need to be labeled east or west

11. Determining Positions on Earth
Measuring Longitude
Local noon or solar noon is when sun is at its highest point at a given location.
Local noon changes one hour for each 150 longitude (3600 in sphere/24 hours in day)
In western hemisphere, local time is earlier than Greenwich time; in eastern hemisphere, local time is later than Greenwich time.

12. Determining Positions on Earth

13. Mapping Fields Isolines Lines connecting points of equal values
Isolines connecting points of equal barometric pressure are called isobars.
Isolines connecting points of equal temperature are called isotherms.
On a topographic field (map), lines joining points of equal elevation are called contour lines.

14. Mapping Fields Gradient
The rate of change of a field quantity between two places
Gradient = change in field value
distance
Example: If a map shows a stream drops 200m between two points 5km apart. What is the gradient?
40 m/km

15. Using Topographic Maps
Contour Maps (topographic maps)
A two-dimensional model, which shows the elevations of various points on the earth surface.
Contour lines pass through points with equal elevations.
The zero contour line is at sea level.
The difference between contour lines is the contour interval.

16. Using Topographic Maps
Map Features
Depressions (holes)
To show these holes hachured lines I I I I I I
are used
First hachure line has the same value as the lowest contour line between which it is found
Each additional hachure line inside the first has a lower value equal to the contour interval.

17. Using Topographic Maps

18. Using Topographic Maps
Map Scale
Relationship between a distance as measured on the map and the actual distance on Earth’s surface
Common ratio is 1:63,360 (1 inch = 1 mile)
Map Slope (Gradient)
Closely spaced contour lines = steep slope
Widely spaced contour lines = gentle slope

19. Using Topographic Maps

20. Using Topographic Maps
Map Key
Includes symbols for various features
Finding Direction
Maps usually oriented so north is top of page
Check for arrow pointing north to verify
Direction of Stream Flow
Streams always flow downhill
The contour lines bend upstream

21. Using Topographic Maps

22. Using Topographic Maps
Profile
Side view of the Earth’s surface
To Make a profile:
Place a strip of paper along the imaginary line on your contour map
Mark the paper wherever it crosses a contour line
Label marks with values of contour lines
Place strip of paper along bottom of graph
Label vertical axis of graph and project marks upwards to locate points of the profile
Connect the marks with a smooth curve

23. Using Topographic Maps