Objectives:Explain several ways how we can test that earth is a sphereDescribe how latitude and longitude are used to define our position on earth’s surfaceUse the position of the north star to determine latitude, and the time of the sun’s maximum height each day to determine longitudePractice finding a location on the globe using latitudes and longitudesImportance of NavigationRely on latitude and longitude to determine locationHypothesis: Earth is a sphere, How do we know?Impossible to prove, only can disproveHypotheses stand or fail on their ability to explain observations, and to successfully predict future observationEx. White swans quote (Karl Popper)i. Lunar Eclipse1. Shadow always roundii. Stars1. Different set of stars depending on being north or south of the equator, would not happen on a flat surface (Aristotle)iii. Sun1. If the world was flat than the Sun should be directly overhead everywhere on the Earth at noon, everyday (Eratosthanes)2. Testa. Two wells (Alexandria and aswan)b. Summer solstice, looked at shadowc. Syene, no shadow (directly above)d. Alexandria, shadow of 7.2 degreese. If the earth was a sphere, then the Higher north, greater degree of shadowf. Wouldn’t be different if the earth was flatWhat is the size of the Earth?Eratosthanes uses trig360 degrees/7.2 degrees = x/50050 x 500 = 25,000 miallows other dimensions to be calculated (radius, area, etc)How do we describe where we are on the planet?Latitude & longitudeGrid system used to precisely describe locations on the earth’s surfaceBased on angular relationships to earth centerExpressed in degrees, each degree is divided into 60 min. each minute divided into 60 secondsPrime Meridian (0 degrees longitude) & equator (0 degrees latitude)Latitude (90 degrees N to 90 degrees S)ParallelsEvery degree of lat. = 60 nautical milesEvery minute of lat. = 1 nautical mileNOT TRUE FOR LONGITUDEDistance between latitude is always constant, but not with longitude because they converge at the polesMost surface area between 30 degrees N and 30 degrees SLongitudeMeridians, intersect at poles180-90 degrees W to 180-90 degrees E of PMPilotingEarliest method of navigationjudging location by landmarks within sight of coastlineDead ReckoningUsed direction and speed of travel to determine approx. positionaided by Sun, moon and stars.Errors cumulativeCelestial Navigation325 BC worked out simple method for determining latitude (Pytheas)determine the angle between the horizon and the North star (Polaris)altitude of Polaris relative to the horizoncloser to equator, Polaris becomes closer to the horizondefines degrees latitudesdevice used to measure the angle called a sextantWhat about longitude?Need to measure time accurately at seaEarth rotates eastward360 degrees/24hrs = 15 degrees/hrneed a reliable clock (chronometer)record time of chronometer at noon (sun directly overhead) compare ship time (noon) with Greenwich time (clock)how many hours ahead or behind Greenwich time?(Difference between your time and GMT) x 15 degrees longitude per hour = your longitudeBehind GMT, Western hemisphereAhead of GMT, Eastern hemisphereObjectives:Describe differences between bathymetry in the ocean and topography on landExplain why detailed sea-floor mapping is an important component of the Law of the SeaPractice calculating sea-floor depths from travel times of sound waves between ship and sea-floorPractice reading and creating bathymetric maps of the sea-floorDescribe the various tools used to determine bathymetryBathymetry: The underwater equivalent of topography. Describes the spatial variations of water depthWhy map the seafloor?Safety of navigation98% of U.S imports by weight come by seadon’t want to get stuck in too shallow waterFor resource exploration and exploitationOil, gas and others minerals, fisheries, habitatModeling ocean processesStorms, tides, circulationHuman curiosityOcean MappingLead Line (2000 BC)Measurement of depth of the seaLimitationsRope not long enoughLimited to shallow water depthsSpot sample, hard to detect sharp drops/spikesCurrent can pull the line so it’s no longer vertical (no accurate)Matthew Maury (father of oceanography) constructed the first ocean-wide Bathymetric map of the North AtlanticOnly 4 pointsIsobaths – connect points of equal elevation/depth below sea levelDarker shades = shallower waterObservationsShallower near landEcho SoundersUse sound as the “line”Sound waves travel at a constant rateBounce off the sea floorMeasure the amount of time it takes for the sound wave to echo backSource & receiver (hydrophone) on hull of shipHigh frequency sound waves travel through the water, reflect off the seafloor and are recorded by the hydrophoneProvide continuous depth profile along a ship’s path.LimitationsOnly two dimensional, can only tell the depth of where the ship goesHard to get timing perfect so that answers are accurateThe longer the depth, the larger the errorSpeed of sound changes with temp, algae, salinity etc.ObservationsFlat region close to shore, “continental shelf”Rapidly drops offMulti-Beam Echo SoundingMany beams of sound in many directions (not just the path of the ship)The Law of the SeaProvides a mechanism for the state to extend its sovereign rights over the resources of the seabed and subsoil of the continental shelfTo establish an extended continental shelf a coastal state (finished on slides)How do we now what the internal structure of the earth is like?p.48-49 in textbookSolid inner core, Liquid outer core, MantleAsthenosphere – lower part of the mantle. Ductile, solid but pliableLithosphere – uppermost portion of the mantle & crustSeismic Waves and EarthquakesReveal the structure of the earthRelease tremendous amount of energy (seimis energy)Seismic waves radiate away from their point of origin (focus)Rayleigh wavestravel along the surface of the earth, cause damageP-wavesfirst wavespressure wavetravel fast through the earthS-waveSide to side motionTravel slowlyDon’t travel through liquidsLike whipping a rope or rugP and S waves bend (refract) when they pass from a material of one density into a material with a different densityMeasure how the velocity of the waves change as they travel through the earthOceanic crust is more dense than the crust of the continentsHow do we know the age of the earth?Radiometric dating of meteorites found on the earth and rocks brought back from the moon (radioactive isotopes and half-lives)oldest rocks on earth about 4