Earth Science Chapter 2 Measuring Earth. Shape of Earth Evidence the Earth is spherical: –Photographs from space –Setting sunlight lingers on treetops,

Earth ScienceEarth Science

Chapter 2Chapter 2

Measuring EarthMeasuring Earth

Shape of EarthShape 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)

Size of EarthSize 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)



• Lithosphere– 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


Determining Positions on EarthDetermining 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).


• 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).


• Measuring Latitude


• 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


• 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.


Mapping FieldsMapping 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.

Mapping FieldsMapping 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

Using Topographic MapsUsing 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.


• 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.



– 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



– 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



• 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


• http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/how_to/topographic_profile.html

Documents

Earth Science Chapter 2 Measuring Earth. Shape of Earth Evidence the Earth is spherical: –Photographs from space –Setting sunlight lingers on treetops,