Class_2_Earth_and_Space_A_new_Wu_Chen.pdf

Class_2_Earth_and_Space_A_new_Wu_Chen.pdf - LSGI1D03 Living...

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Unformatted text preview: LSGI1D03 Living on a Dynamic Earth Class 2 Earth and Space Part A Class 2 1 Content • • • • Class 2 The Formation of the Earth The Structure of the Earth The Shape of the Earth The Magnetic Field of the Earth 2 The Birth of the Earth • The earth was formed together with the solar system around 4.6 billion years ago § § § Class 2 From cosmos – debris of Supernova The debris collided with each other When became large enough, gravity started to work 3 Collision with mini planets • The moon was formed 30 million years late after the earth was born • For inner planets, Mercury and Venus have no moons, and Mars has only two small asteroid-­sized objects orbiting it • The Birth of the Earth Class 2 4 The Structure of Earth Class 2 5 The Earth • A planet § § § § § Class 2 Distance from sun: ≈ 15010& (1 ) Travelling at: 28.910/ 12 Diameter: 12.8103 Mass: 6.01056 How the mass is estimated? 6 Structure of Earth • Made up of several layers § § § § Inner core Outer core Mantle Crust • Only planet to have large amounts of liquid water and oxygen Class 2 7 Structure of Earth • Other layers § Lithosphere • Crust plus upper section of solid Mantle • 0 to 100 depth § Asthenosphere • Viscous part of the upper Mantle • 75 to 200 • Responsible for floating the continents Class 2 8 Structure of Earth Source Mohorovičić discontinuity Transition zone Core-­Mantle Boundary Bullen discontinuity Class 2 9 Structure of Earth • Inner core § § § § Studied via seismology Spherical Radius: 1,216 Solid nickel-­iron ( − ) alloy • Crystalline structure § § Temperature: 5,500° May have two layers − will melt at about 1,500° on the surface of Earth. Why is it solid at the Core? • See BBC § Class 2 The journal article 10 Structure of Earth • Outer core § § § § Studied via seismology Thickness: 2,266 Fluid iron and nickel Temperature • Inner: 6,100° • Outer: 4,400° § Class 2 Interaction with Inner Core creates currents responsible for Earth's magnetic field Source 11 Structure of Earth • Mantle § Two layers • Lower Mantle § § 2,600 Viscous magma • Silica (5 ) and Magnesium Oxide () • Upper Mantle § § Class 2 Asthenosphere -­ ductile (plastic) • Supports the continental plates Lithosphere -­ rigid • Transports the continental plates 12 Mantle Convection and Plumes • Convection Class 2 • Plumes 13 Structure of Earth • Crust § Two components • Continental § § 10 to 75 thick Granitic rock of feldspar and quartz • Felsic () • Low density • Oceanic § § Class 2 5 to 7 thick Basaltic rock • Mafic () • High density 14 Structure of Earth Source Source Source Class 2 15 Structure of Earth • Crust § Consists of the tectonic plates • 7-­15 major • 3-­11 minor • A large number of microplates § Plate tectonics • Emerged from the theory of Continental Drift of 1910's • Confirmed in 1950's by evidence of sea floor spreading § Plates constantly in motion • Between 2 and 15 per year Class 2 16 Structure of Earth Source Class 2 17 Movement of Tectonic Plates Class 2 18 Earth's shape and size The domain of geodesy Class 2 19 Earth's shape and size • There are some people who believe Earth is flat § The Flat Earth Society (www) • "the earth is a flat disk centered at the North Pole and bounded along its 'southern' edge by a wall of ice, with the sun, moon, planets, and stars only a few hundred miles above the surface of the earth" Class 2 20 Earth's shape and size • Proven to be curved in about 200 BC by Eratosthenes (www) § § § Calculated the circumference of Earth Tilt of Earth's axis First map of the world using meridians of longitude and parallels of latitude • Eratosthenes (YouTube) Class 2 21 Earth's shape and size Note the text says 7.5˚ Source Class 2 22 Earth's shape and size • Eratosthenes' circumference § 252,000 = 46,620 • 1 = 185 • Modern measurements give the circumference as 40,075 making Eratosthenes value 16% too large • Actual circumference depends on where and how it is measured Class 2 23 Earth's shape and size • The actual shape § § § § § Class 2 3D shape A fluid with unequal distributions of land and ocean masses Constantly changing shape Constantly varying gravity field Difficult to accurately assign geometric parameters to describe its shape 24 Earth's shape and size Source Source Source Class 2 25 Earth's shape and size • Approximations § § § Sphere () Oblate spheroid (ellipsoid, and ) Scalene (tri-­axial) ellipsoid (, , ) • For most practical purpose an oblate spheroid is used § An ellipse rotated about its minor () axis • A prolate spheroid is an ellipse rotated about its major axis () Class 2 26 Earth's shape and size See Ellipsoid.cdf You’ll need to install the cdf player Note that , , = , , Minor semi-­axis, z y Major semi-­axis, Class 2 x 27 Earth's shape and size • The most widely used parameters are § Equatorial radius, = 6,378,137 U1V § Flattening, = § Polar radius, = 6,356,752 U = 1/298.257223563 • This is called WGS-­84 and is the basis of GPS positioning • The difference between Equatorial and Polar radii is just 21,385 or 0.3% • Why is Earth oblate? Class 2 28 Earth's shape and size • What dimensions can be used for a spherical Earth? § § § § § Equatorial radius, : 6,378,137 Polar radius, : 6,356,752 UXV Mean radius, 5 : 6,367,444 Quadratic mean radius, Volumetric radius, 5 . : 6,371,001 Authalic radius, Sphere of same surface area Class 2 6 : 6,372,797 [ Sphere of same volume § /.U Y XV Y UY X \.]Y \a \Y ^]Y ._` \Y ^]Y 5 : 6,371,007 29 Earth's shape and size • The actual shape of Earth would be oblate if it was homogeneous • Land and water § § Have different densities Are unevenly distributed • Gravity varies from place to place • The physical shape is something different… Class 2 30 Earth's shape and size Source Class 2 31 Structure of Earth Any similarities? Source Class 2 32 Earth's shape and size Source Class 2 33 Earth's shape and size • As gravity controls so much of our lives using it to define a reference surface is reasonable • That surface is called the Geoid § The equipotential surface that represents the gravitational potential of mean sea level • What is sea level? (YouTube) Class 2 34 Earth's shape and size • Gravitational potential energy, = 1b.c.d See Hyperphysics § § § § e = gravitational constant = mass of Earth = mass of another body = separation of the two body's centres of mass • What happens over land and sea? Class 2 35 Earth's shape and size under mountains is larger so is larger for the same Geoid Geoid height, N Ellipsoid under the oceans is smaller so is smaller for the same N Class 2 36 Earth's shape and size Class 2 37 Earth's shape and size A map of (m) Source Class 2 38 Coordinate System of the earth Longitude and latitude Class 3 39 Global Geodetic system • Origin: mass centre of the earth • Z axis: rotation axis of the earth • X,Y axes: on the equator Class 2 40 Longitude and latitude • A system for identifying the location of a point on ellipsoid (the Earth model) surface • When drawn on a map § § Longitude shows position east and west Latitude show position north and south • Together they define the graticule Class 3 41 Longitude and latitude Longitude Latitude Source Class 3 42 Longitude and latitude • Assume a spherical Earth • North and South Poles define Earth's rotational axis • The Equator § § Class 3 The line of intersection between a plane normal to and bisecting the rotational axis and Earth's surface Equatorial plane contains Earth's centre 43 Longitude and latitude North Pole Equator South Pole Class 3 44 Longitude and latitude • Longitude (, lambda) § An angle measured in the plane of the Equator between • A circle containing the Poles and the Observatory at Greenwich, London (Prime Meridian, = 0°) • A circle containing the Poles and the place of interest § § § Class 3 Circles are called meridians Positive east of Greenwich, negative west Range = ±180° Source 45 Longitude and latitude • Latitude (, phi) § § § § § § Class 3 An angle measured from the Equator along the meridian containing the point of interest Equator = 0 All points on a circle parallel to the Equator have the same Circle is called a parallel Positive north, negative south Range = ±90° 46 Longitude and latitude Pole Parallels of latitude Greenwich Prime Meridian Meridians of longitude Equatorial plane Maling Class 3 47 Longitude and latitude • Units § § Prime unit is degrees of arc, D° Sub units are either • Decimal degrees, . ° • Minutes and seconds, ° l . " Class 3 48 Longitude and latitude • Distances § § Using a spherical Earth of = 6,372 Latitude • = . Δ § Δ is in radians (1° = p 2qr = 0.0175 ) • 1° = 111. 2 , 1l = 1.85 , 1" = 30.9 § Longitude • On the Equator, same as for latitude • Along a parallel = . . Δ § § Class 3 At = 20°, 1° = 104.5 , 1l = 1.74 , 1" = 29. 0 At = 80°, 1° = 19.3 , 1l = 322 , 1" = 5. 4 49 Earth’s magnetic field Class 3 50 Earth’s magnetic field • Some parts of Earth rotate faster than others § § § § Class 3 Interaction between Mantle, Outer Core and Inner Core produce a geomagnetic field Solid Inner Core heats the fluid Outer Core creating convection currents in the Mantle due to different rotation rates Iron content produces magnetic fields Strength varies over Earth's surface 51 Earth’s magnetic field Source Earth's Magnetism (YouTube) Source Class 3 52 Earth’s magnetic field • Magnetic field’s axis does not coincide with rotational axis § The difference in direction is declination • Varies with location on Earth’s surface • Magnetic Poles are where the magnetic axis intersects Earth’s surface § Definition of poles depends on the field’s inclination • North Pole has field going "down" • South Pole has field going "up" Class 3 53 Earth's magnetic field Declination Inclination Source Class 3 54 Earth's magnetic field • Location of the magnetic poles constantly changing § § Reported that they are moving at about 65 per year Poles (polarity) have reversed many times • Due to changes within Earth’s core • Polarity changes "frequently" (www) Source Million years ago Black = same polarity as now Class 3 55 Class 2 56 Earth’s magnetic field Source Class 3 57 • Geomagnetic field is crucial for the survive of all living creatures on the Earth • Geomagnetic field is an important tool for navigation Class 2 58 Earth's magnetosphere Class 3 59 Earth's magnetosphere • The geomagnetic field extends into space by about 58,000 • Shields Earth from harmful radiation § § Solar wind Cosmic rays • Charged particles (electrons and protons) trapped by the magnetic field § Form Van Allen Belts • Van Allen Radiation Belt (YouTube) Class 3 60 Earth's magnetosphere Source Source Class 3 61 Earth's magnetosphere • Interaction of Van Allen Belts with Solar Wind produces the Magnetosphere Source Class 3 62 Earth's magnetosphere • The trapped particles come into contact with Earth's atmosphere where they're directed towards the Poles • Charged particles ionise and excite atmospheric particles and produce light § Creates the phenomenon of auroras • Northern hemisphere: Aurora Borealis • Southern hemisphere: Aurora Australis • Intensity depends on amount of particles in the Solar Wind Class 3 63 Earth's magnetosphere Source Source Source Source Class 3 64 ECL English Requirements • "Introducing English Writing Requirement Option 2" https://youtu.be/bVBISo2EpDQ Class 2 65 Tutorial Videos • • • • • • Future space technologies (www) Earth's Magnetism (YouTube) Origin of Earth’s Magnetic Field Why Earth's Magnetic Shield Matters How gravity shapes Planet Earth The Birth of the earth Class 2 66 ...
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