Measuring the Earth Chapter 2

Models Physical models use observations of sight to provide us with information. Mental models represent ideas or images of something in your mind. Laboratory models are used to simulate natural events. Mathematical models are formulas and equations. Graphical models are used to simplify relationships between variables.

Size 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 Structure The earth is divided into several parts, or “layers”. –T–The top layer, the c cc crust, is about 10km thick beneath the oceans and 65km thick beneath the continents. –T–The m mm mantle is about 2850km thick. –T–The o oo outer core is about 2100km thick. –T–The i ii inner core is about 1400km thick.

Earth’s Structure

Outer Spheres lithospherehydrosphere atmosphereThe outer layer composed of the lithosphere, hydrosphere, and atmosphere. 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 Earth Coordinate systems are grid-like systems of imaginary lines that determine locations on Earth’s surface. Latitude is the distance, in degrees, north or south of the equator. –T–The E EE Equator is 0o and the N NN North Pole is 90o N latitude and the S SS South Pole is 90o S latitude. –P–P–P–Parallels of latitude – all lines are parallel. –A–A–A–Altitude of Polaris = your latitude. Longitude is the distance, in degrees, east or west of the P PP Prime Meridian 0o

Latitude and Longitude

Measuring Longitude Chronometer Prime Meridian (Greenwich Mean Time – G.M.T.)solar timeChronometer is an accurate clock which keeps the time at the Prime Meridian (Greenwich Mean Time – G.M.T.) and the solar time at any other meridian. Solar noonSolar noon is when the sun is a it’s highest altitude.

Mapping Fields IsolinesIsolines are lines connecting points of equal value. isobars, isotherms, contour lines –Examples are isobars, isotherms, contour lines. Contour linesContour lines are lines on a map that connect points of equal elevation.

Gradient gradientslopeThe gradient, or slope, is the rate of change of a field quantity between two places. Gradient = change in value change in distanceGradient = change in value change in distance

Using Topographic Maps Topographic mapscontour mapsTopographic maps (contour maps) show the elevation of various points on the Earth’s surface. contour intervalThe contour interval is the difference in value between contour lines; zerosea level –The zero contour line is at sea level.

Contour Lines

Topographic Map

Map Features Depressions are holes dug into Earth’s surface and these are shown on a map by h hh hatchured lines. Direction is indicated on most maps by an arrow to indicate north. Map Scale is the ratio of distance on the map to distance on the earths surface. –E–Ex: 1 :63,360 means that one inch on the map equals 63,360 inches, or one mile, on Earth’s surface.

Map Features

Profiles profileA profile is a side view of the Earth’s surface.

Map Profiles

Map Slope Map slope, or g gg gradient, is the rate of change of elevation between two points. Gradient = change in value (height) change in distance (a to b) The c cc closer lines are together the steeper the slope.

Different Gradients (Slopes)

Stream Flow Streams always flow downhill. To determine direction of stream flow examine the contour lines wherever a stream crosses them. bendspoint upstream. –The bends in the contour lines point upstream.