Chapter 2 Measuring Earth 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 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

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 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).

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/geog101/textbook/how_to/topographic_profile.html