Transcript chapter 2
Chapter 2 Statistics ◦ Oblate spheroid – a slightly flattened sphere ◦ Spins on its axis which causes the polar regions to flatten and equatorial zone to bulge Axis: imaginary straight line running through the Earth from North to South Pole Hydrosphere ◦ All the Earth’s water ◦ 71% covered by water 97% in the salty oceans 3% fresh water found in lakes, rivers, and streams, glaciers and polar ice sheets Atmosphere ◦ Blanket of gases that surround the Earth 78% Nitrogen 21% Oxygen 1% other gases (argon, carbon dioxide, & helium Discoveries about earth’s interior made through seismic waves ◦ Vibrations that travel through the earth Zones ◦ Crust Outermost Zone ◦ Mantle Below the Crust ◦ Core Below the Mantel 1% of the earth’s mass ◦ Mass: the amount of matter in an object Oceanic Crust ◦ 5 km to 10 km thick Continental Crust ◦ 15 km to 80 km ◦ Thickest beneath high mountain ranges Zone of Rock nearly 2,900 km thick 2/3 of earth’s mass Regions ◦ Lithosphere – uppermost; cool and brittle ◦ Asthenosphere – just below the lithosphere; solid rock that flows (plasticity) Center of the earth Mostly Iron ◦ Outer Core – Dense liquid layer ◦ Inner Core – Dense solid sphere 1/3 of earth’s mass P Waves ◦ Primary waves ◦ Travel through liquids, solids, and gases ◦ Travel faster than S waves S Waves ◦ Secondary waves ◦ Travel through solids only Speed and Direction effected by composition Both travel faster through more-rigid materials Seismic waves Change in the speed of the waves marks the boundary between the crust and the mantle Increase in speed at the Moho indicates the earth’s mantle is denser than its crust Below Moho a decrease in seismic-wave speed marks the boundary between lithosphere and asthenosphere Then increase in speed, then slow, then disappear Overall?? Locations on the earth’s surface where neither S waves nor P waves are detected or where only P waves are detected Occur because the materials that make up the earth’s interior are not uniform in rigidity Differing rigidities – waves bend and change direction Two magnetic poles Northern Geomagnetic and Southern Geomagnetic Poles Magnetosphere: region of space, effected by earth’s magnetic field Theorize - Liquid iron in the outer core Sun and the Moon have magnetic fields, but little iron Weight: measure of the force of the pull of gravity on an object. Isaac Newton Gravity – the force of attraction that exists between all matter in the universe Law of Gravity – the force of attraction between any two objects depends upon their masses and the distance between them Mass does not change, but weight does with location. Force of gravity decreases as distance from core increases Mass: amount of matter in an object. Revolution – movement of the earth around the sun ◦ 365.24 days Rotation – the earth spinning on its axis ◦ 24 hours/1 day ◦ West to East ◦ Sun rises in the East; Sets in the West ◦ Nighttime in the Western hemisphere = Daytime in the Eastern hemisphere Orbit (path around the sun) slightly elliptical Closest point to the sun – Perihelion ◦ January 3rd Farthest point from the sun – Aphelion ◦ July 4th Earth’s axis tilted 23.5˚ As earth revolves axis point does NOT change – points to North Star North pole tilts toward sun ◦ Northern hemisphere Longer periods of daylight Sun’s rays strike at higher angles ◦ Southern hemisphere Shorter periods of daylight Sun’s rays strike at lower angles South pole tilts toward sun…what happens. Changes in the angles at which the sun’s rays strike the earth’s surface & changes in daylight hours cause seasons North pole tilted away = less daylight hours ◦ Why? Sun’s rays on N.H. are lower ◦ Season = Winter ◦ What would it be like in the Southern Hemisphere? Winter Summer Fall Spring Summer Solstice ◦ June 21 or 22 ◦ North Pole tilts toward sun ◦ Sun’s rays strike the earth at 90˚ angle along the Tropic of Cancer ◦ Most hours of daylight ◦ Farther north of equator = more daylight hours. ◦ North of Arctic Circle = 24 hours of daylight ◦ Southern Hemisphere? December 21 or 22 North Pole tilts away from sun Sun’s rays strike the earth at 90˚ angle along the Tropic of Capricorn Fewest hours of daylight hours Winter in the Northern Hemisphere Farther north less daylight hours North of Arctic Circle 24 hours of darkness Southern Hemisphere? • Equinox – “equal night” • Daylight/darkness are equal everywhere on earth • North pole neither tilts toward nor away • Sun’s rays strike the earth at 90˚ angle along the equator. Autumnal ◦ September 22 or 23 ◦ Fall season in the Northern Hemisphere Vernal ◦ March 21 or 22 ◦ Spring season in the Northern Hemisphere North Star or Polaris – axis points toward! Precession – caused by forces acting on a spinning body ◦ Causes the earth’s axis to move slowly in a circle ◦ Complete one full circle every 26,000 years ◦ Polaris continues for many years Sun is the basis for measuring time 12:00 noon sun is highest in the sky Sun movement from east to west ◦ Sun appears highest over different locations at different times ◦ Standard Time Zones Noon is set as the time when the sun is highest over the center of that zone Earth’s circumference equals 360˚/24 hours which means earth rotates at a rate of 15˚ each hour. 24 hour time zones cover 15˚ Time in each zone is one hour earlier than the time zone to its east International Date Line Daylight Saving Time ◦ Longitude line through the Pacific Ocean ◦ Date changes from one day to the next ◦ U.S. set 1 hour ahead for more daylight hours ◦ Spring time ◦ Ends in Fall, return to Standard time ◦ Spring forward; Fall back!! Satellite – any object in orbit around another body with a larger mass ◦ Put into orbit by powerful computerguided rockets ◦ Earth’s gravity holds the satellite in orbit ◦ The higher the orbit of a satellite, the lower the speed needed for it to stay in orbit. Geosynchronous Orbit ◦ Directly above the earth’s equator and moving in the direction of the earth’s rotation ◦ Always remains at the same point above the equator and appears stationary ◦ Useful for communication Carries satellite over the earth’s North and South poles Satellite passes over a different portion of the earth’s surface during each revolution Mapping the earth’s surface American Scientific Satellites ◦ Landsat Polar orbit Images of earth’s surface, cities, vegetation regions, and/or rock types etc… ◦ GPS Global Positioning System Network of satellites used for accurate navigation of ships and aircraft