Earth Science Chapter 2 Measuring Earth Shape of

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 o. N latitude • South Pole = 90 o. S 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 200 m between two points 5 km 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 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 g 101/textbook/how_to/topographic_profile. html