Download Chapter 2: Measuring Earth - Westmoreland Central School

Earth Science
Chapter 2
Measuring Earth
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)
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)
Size of Earth
Size of Earth
• 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
Size of Earth
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 latitudelongitude 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).
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).
Determining Positions on Earth
• Measuring Latitude
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
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.
Determining Positions on Earth
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.
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
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.
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.
Using Topographic Maps
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
Using Topographic Maps
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
Using Topographic Maps
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
Using Topographic Maps
• http://www.uwsp.edu/geo/faculty/ritter/geo
g101/textbook/how_to/topographic_profile.
html