Journey to the Center of the Earth Earth s surface Our experience with Earth is limited to its surface Yet earth has a complicated interior Earth is characterized by An internally generated magnetic field Solid and liquid surfaces A gaseous envelope A layered interior The Solar System Human perception have changed Early history planets as moving lights 1600s 1st telescopes saw hazy spheres today a complex evolving system Space probes have photographed and analyzed planets Scientists have hypothesized likely origins of the solar system Earth and the Solar System What would solar system visitors notice Magnetic field Atmosphere Surface features Continents Oceans Polar ice caps Evidence of humanity The Celestial Neighborhood Interstellar space a vacuum with a virtual absence of matter The amount of matter greatly increases approaching the Sun The Sun ejects matter outward into space as the solar wind Solar Wind Charged particles Stream outward in all directions Consist of protons and electrons A small percentage of the solar wind impinges upon Earth Magnetic Field The earth has a prominent dipolar magnetic field The field has north and south ends Magnetic flux has a direction that flows N to S Magnetic field lines Extend into space Weaken with distance Create a shield around Earth the magnetosphere The Van Allen Belts The solar wind is deflected by the magnetosphere Near the Earth the stronger magnetic field forms the Van Allen belts which arrest deadly solar cosmic radiation Aurorae Some ions escape Van Allen belts These ions are pulled to the magnetic poles The ions create light in the upper atmosphere Spectacular aurora follow solar flares Aurora borealis northern lights Aurora australis southern lights The Atmosphere Earth has a well developed atmosphere Densest at sea level the atmosphere thins upward 99 of atmosphere is below 50km the rest is between 50 and 500 km The atmosphere is layered Troposphere 0 14km Mixing layer Weather is limited to this layer Tropopause 14018 km Stratosphere 18 50km Sea level atmospheric pressure 1 atm 1 04 kg cm2 14 7 pounds per square inch psi 1 0 bar The atmosphere is mostly nitrogen Oxygen was absent from the atmosphere before 2 5 Ga Surface features Earth surface sis dominated by water and land Water is a part of the hydrosphere Surface water Ground water Glacial ice Impact craters occur rarely on Earth Removed by weathering and erosion Unlike other planets in the solar system Earth s surface reveals high continents and low ocean basins Position due to the differing buoyancy of each type of crust Hypsometric curve Most land lies within 1 km of sea level Most ocean floors are close to 5km depth Extremes of depth or height are rare Elemental Composition 90 of Earth is comprised of 4 Elements Iron 35 Oxygen 30 Silicon 15 Magnesium 10 The remaining 88 naturally occurring elements Form 10 of Earth Earth Materials Elements combine in a variety of Earth materials Organic compounds Carbon containing compounds Most are residue from once living creatures Include wood peat lignite coal and oil Geologically rare decomposes in contact with oxygen Mineral Inorganic crystalline solids Comprise rocks and hence most of the Earth Most rocks on Earth are silicates based on Si and O Glasses non crystalline mineral like matter Rocks Aggregates of minerals There are many types Igneous cooled from a liquid melt Sedimentary debris from pre existing rock or minerals precipitated out of a water solution Metamorphic rock altered by pressure and heat Metals solids made of metallic elements Melts rocks that have been heated to a liquid Magma molten rock beneath the surface Lave molten rock at the surface Volatiles materials that turn into gas at the surface Volatiles are released from volcanic eruption A layered Earth We live on the thin outer skin of earth Early perceptions about Earth s interior were wrong Open caverns filled with magma water and air Furnaces and flames We now know that Earth is comprised of layers The crust The mantle The core outer and inner core Several clues indicate a layered structure Density Average density greater than surface density Density must increase with depth Shape a rotating sphere requires centered mass Mass away from center would result in a flattened disk Solid interior surface doesn t undulate from tidal forces Earthquakes clues Earthquake energy transmitted as seismic waves that pass through earth Seismic waves have been used to probe the interior Waves velocity changes with density Velocity changes give depth of layer changes Earth and other planets have layered interiors Changes with depth Pressure Temperature Earth s interior layers Crust Continental Oceanic Mantle Upper Lower Core Outer liquid Inner solid The crust The outermost skin of Earth with variable thickness Thickest under mountain ranges 70km 40 miles Thinnest under mid ocean ridges 3km 2 miles The Mohorovicic discontinuity is the lower boundary Separates the crust from the upper mantle Discovered in 1909 by Andrija Mohorovicic Marked by a change in the velocity of seismic P waves Two types of crust Continental crust underlies the continents Average rock density about 2 7 g cm3 Average thickness 35 40 km Granitic in composition Oceanic crust underlies the ocean basins Density about 3 0 g cm3 Avg Thickness 7 10 km Basaltic in composition Two types of crust Crustal density controls surface position Continental crust Less dense floats higher Oceanic crust More dense floats lower Crustal composition 98 5 of the crust is comprised of just 8 elements Oxygen is by far the most abundant element in the crust This reflects the importance of silicate minerals As a large atom oxygen occupies 94 of crustal volume Earth s mantle Solid rock layer between the crust and the core 2 885 km thick the mantle is 82 of Earth s volume Mantle composition is the ultramafic rock peridotite Below 100 150km the rock is hot enough to flow It convects hot mantle rises cold mantle sinks Three subdivisions upper transitional and lower An iron rich sphere with a radius of 3 471 km 2 components with differing seismic wave behavior The core Outer core Liquid iron nickel sulfur 2 255 km thick density 10 12 g cm3 Inner core solid iron nickel alloy radius of 1 220 km density 13 g cm3 Flows in the outer core generates the magnetic field Lithosphere the outermost 100 150 km of Earth Behaves as a non flowing rigid material The material that moves as tectonic plates Made of 2 components crust and part of upper
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