Measuring the EarthMeasuring the Earth

Chapter 2

ModelsModels

• Physical modelsPhysical models use observations of sight to provide us with information.

• Mental modelsMental models represent ideas or images of something in your mind.

• Laboratory modelsLaboratory models are used to simulate natural events.

• Mathematical modelsMathematical models are formulas and equations.

• Graphical modelsGraphical models are used to simplify relationships between variables.

Size of the EarthSize of the Earth

• Eratosthenes, about 200 BC, made a very accurate determination of the Earth’s circumference. (39,000 km)– The earth’s actual circumference is

equal to 40,076 km.

Earth’s StructureEarth’s Structure

• The earth is divided into several parts, or “layerslayers”.

– The top layer, the crustcrust, is about 10km thick beneath the oceans and 65km thick beneath the continents.

– The mantlemantle is about 2850km thick.– The outer coreouter core is about 2100km thick.– The inner coreinner core is about 1400km thick.

Earth’s StructureEarth’s Structure

Outer SpheresOuter Spheres

• The outer layer composed of the lithospherelithosphere, hydrospherehydrosphere, and atmosphereatmosphere.

• LithosphereLithosphere is the rock near Earth’s surface that forms continuous solid shell around the Earth.

• HydrosphereHydrosphere is the thin layer of water resting on the lithosphere. (70% of the Earth’s surface)

• AtmosphereAtmosphere is a relatively thin shell of gasses, held to the Earth’s surface by gravity, that surrounds Earth.

Determining Positions on Determining Positions on EarthEarth

• Coordinate systemsCoordinate systems are grid-like systems of imaginary lines that determine locations on Earth’s surface.

• LatitudeLatitude is the distance, in degrees, north or south of the equator. – The Equator is 0Equator is 0oo and the North Pole is 90North Pole is 90oo N N

latitude and the South Pole is 90South Pole is 90oo S S latitude.– Parallels of latitudeParallels of latitude – all lines are parallel.– Altitude of PolarisAltitude of Polaris = your latitude.

• LongitudeLongitude is the distance, in degrees, east or west of the Prime Meridian 0Prime Meridian 0o o

Latitude and LongitudeLatitude and Longitude

Measuring LongitudeMeasuring Longitude

• ChronometerChronometer is an accurate clock which keeps the time at the Prime Prime Meridian (Greenwich Mean Time – Meridian (Greenwich Mean Time – G.M.T.)G.M.T.) and the solar timesolar time at any other meridian.

• Solar noonSolar noon is when the sun is a it’s highest altitude.

Mapping FieldsMapping Fields

• IsolinesIsolines are lines connecting points of equal value.– Examples are isobars, isotherms, isobars, isotherms,

contour linescontour lines.• Contour linesContour lines are lines on a map

that connect points of equal elevation.

GradientGradient

• The gradientgradient, or slopeslope, is the rate of change of a field quantity between two places.

• Gradient = Gradient = change in valuechange in valuechange in distancechange in distance

Using Topographic MapsUsing Topographic Maps

• Topographic mapsTopographic maps (contour contour mapsmaps) show the elevation of various points on the Earth’s surface.

• The contour intervalcontour interval is the difference in value between contour lines;– The zerozero contour line is at sea levelsea level.

Contour LinesContour Lines

Topographic MapTopographic Map

Map FeaturesMap Features

• DepressionsDepressions are holes dug into Earth’s surface and these are shown on a map by hatchured lineshatchured lines.

• DirectionDirection is indicated on most maps by an arrow to indicate north.

• Map ScaleMap Scale is the ratio of distance on the map to distance on the earths surface.– Ex: 1:63,3601:63,360 means that one inch on the map

equals 63,360 inches, or one mile, on Earth’s surface.

Map FeaturesMap Features

ProfilesProfiles• A profileprofile is a side view of the Earth’s

surface.

Map ProfilesMap Profiles

Map SlopeMap Slope

• Map slopeMap slope, or gradientgradient, is the rate of change of elevation between two points.

Gradient = Gradient = change in value (height)change in value (height) change in distance (a to b) change in distance (a to b)

The closercloser lines are together the steepersteeper the slope.

Different Gradients Different Gradients (Slopes)(Slopes)

Stream FlowStream Flow

• Streams always flow downhill.

• To determine direction of stream flow examine the contour lines wherever a stream crosses them.– The bendsbends in the contour lines point point

upstreamupstream..