Earth

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Earth

• The Model Planet

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If you encountered another planet,what would you
want to learn about it?

• Basic physical parameters
• How old is the planet? How was it formed?
• How is it structured internally? Externally?

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Learning more

• Does it have a magnetic field? How strong is it?
  How is it structured? What does it tell us
  about the planets interior?
• How is its atmosphere structured? Of what is it
  made? What are its weather patterns? How does
  the atmosphere help control the planets energy
  budget?

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Learning more (2)

• Has the atmosphere always been the same as it is
  now? How has the atmosphere interacted with the
  surface?
• What kinds of physical processes have produced
  the planets landforms?
• Is there life on the planet? How does it
  interact with the various ecosystems?

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Physical Properties
Diameter 12,756 km at the equator
Why specify at the equator?
Because the polar diameter is only 12,697 km
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Physical Properties
The bulging at the equator and flattening at The
poles is called OBLATENESS. Its due to the
rotation of the planet.
Earth is the most spherical (least oblate) of all
the planets.
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Physical Properties

• Volume 1.1 trillion cubic kilometers (km3)
• Mass 5.97 x 1024 kilograms

Mt. Everest is about than 2400 km3http//experts.
about.com/q/Geography-1729/Volume-Mount-Everest-1.
htm
This is equal to about 81 moons!
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Physical Properties

• Density 5500 kg/m3 or 5.5 g/cm3
• We compare the density of materials like rocks
  metals to the density standard WATER!
• Waters density is 1.0 g/cm3

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Physical Properties

• Most rocks have densities between 2.5 and 4.0
  g/cm3
• Most metals have densities greater than 6.0 g/cm3
• Iron is 7.8 g/cm3
• Nickel is 8.9 g/cm3

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Physical Properties

• The density of an object reflects its
  composition.
• What does Earths density tell you about its
  composition?

Earth must be made of a combination of rocks and
metals.
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How old is the Earth?

• About 4.6 billion years.
• The oldest rocks are found on the north slope of
  Canada, the Canadian Shield. These rocks are 4.0
  billion years old. They were dated from the
  radioactive decay of uranium into lead.
• The other 0.6 billion years is an estimate of how
  long it took the earth to form.

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How was the earth formed?

• Accretion
• Differentiation
• Interior Structure
• Evidence, or How sure are we?

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• A rotating cloud of gas dust
• a nebula

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• Rotation causes the nebula to flatten

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• A star ignites in the center and a
• temperature gradient forms.

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• Solid chunks, called planetissimals,
• begin to condense close to the star.

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Accretion

• Planetissimals (dust-sized to small moon-sized
  solid bodies) begin to form near the sun.
• Gravity attracts planetissimals into larger and
  larger bodies. Planets begin to grow.
• Most of the stuff of planetissimals is rock
  (silicates Na, Ca, Mg, O, Si) and heavy metals
  (Fe, Ni).

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Differentiation

• As earth grows in size, its gravity grows too
• It begins to pull in other planetissimals, which
  impact on its surface.
• What happens when you repeatedly hit a piece of
  metal with a hammer?

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Differentiation

• All the heat generated by planetissimals
  impacting on the surface, plus the heat generated
  by radioactive decay in the young earths
  interior causes the entire earth to melt.

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Differentiation

• When the entire earth is molten, the heavy
  elements (iron, nickel) sink to the interior.
• The lighter materials (granite-type rocks) rise
  to the surface.
• The medium density rocks (basalt-type) ends up in
  the middle.
• Layers form core, mantle, crust.

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Molten Earth, heated by impacts
radioactive decay.
Differentiated (layered) Earth after cooling.
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Interior Structure

• Inner Core (kept solid by the immense pressure of
  all the material on top of it.)
• Outer Core (less pressure allows it to be a
  liquid.)
• Mantle
• Asthenosphere
• Lithosphere
• Crust

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Solid Inner Core 2400 km diameter Iron Nickel
Liquid Outer Core 2270 km thick Iron Nickel
Crust 20-100 km thick Granitic rocks Feldspars
Mantle 2900 km thick Basaltic rocks Olivine,
Pyroxene
Interior section of mantle is a thick fluid
called the asthenosphere. The outer mantle the
crust are rigid and are collectively called the
lithosphere.
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More about the layers

• The difference between the mantle and the crust
  is based on chemical composition.
• The difference between the asthenosphere and the
  lithosphere is based on viscosity (the ability to
  flow under pressure.)

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How do we know?

• What evidence do we really have that the interior
  of the earth is the way we think it is?
• Deep mines are hot!
• Heat and molten material escape from volcanos and
  geysers.
• Earthquake waves

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Earthquake Waves

• When an earthquake occurs it produces 2 types of
  waves
• P or primary waves. These are waves of
  compression of the rock. They travel fastest.
• S for secondary or shear waves. The rock moves
  up down or sideways.

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Earthquake waves

• P waves are capable of traveling through both
  liquids and solids, so they travel through mantle
  and cores.
• S waves cant travel through liquids, so they
  stop when they hit the outer core.
• Look closely at the next diagram.

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Cornell Univ.
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How bigs that core?

• With the right placement of seismometers around
  the earths surface, we get a good estimate of
  the size of the outer core.
• The size of the inner core is calculated from
  theory.

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Earths Magnetic Field

• Why does Earth have a global or world-wide
  magnetic field, while other similar planets
  either have no magnetic fields or very different
  kinds of fields?
• Why should we care about Earths magnetic field?
  What does it do for us?

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Earths Magnetic Field

• Magnetic fields are made wherever there is an
  electric current, that is the movement of
  electrons.
• In a regular bar magnet, the magnetic field comes
  from the electrons orbiting around the nuclei of
  the iron atoms. All the electrons orbit in the
  same direction.

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Earths Magnetic Field

• In the earth, electrical currents run through the
  molten iron core. Friction within the molten,
  flowing iron knocks electrons off iron atoms.
• The molten iron flows at about 0.8 inches per
  second, but the electrical currents can flow
  faster.

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Earths Magnetic Field

• The electrical currents within the earth cause
  earth to act like a gigantic electromagnetic
  generator.
• This is called the Dynamo Theory of magnetic
  field generation.

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A little more info

• The earths magnetic field isnt strong enough
  for us to feel, but many animals can sense it and
  even use it to navigate. Its only about 0.4
  Gauss, much weaker than a small magnet you can
  hold in your hand.
• On average, the North South poles flip every
  390,000 years. There have been 9 flips in the
  past 3.5 million years.

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The poles flip ?

• No one knows how long the process takes, maybe a
  few years, maybe a few minutes.
• Every so often, what was the North magnetic pole
  suddenly becomes the South magnetic pole.
• Lava that cools quickly on the sea floor records
  these flips and lets us date them.

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Stripes of different magnetic polarityform in
the rocks as the lava from themid-ocean ridge
cools.
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Strange Things Going On

• Earths magnetic field is NOT aligned with its
  rotational axis.
• The magnetic field is tilted 12o to the
  rotational axis, and doesnt even pass directly
  through the center of the earth.
• Does this mean that the electrical currents dont
  flow evenly and uniformly inside the earth? Is
  there turbulence inside?

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Magnetic Fields in Space

• Earths magnetic field extends 7-10 times the
  earths diameter outward from the earth.
• The earths magnetic field would be spherical,
  but the solar wind compresses it on the side
  closest to the sun, and stretches it out into a
  long tail on the side opposite the sun.
• Overall, its kind of tadpole shaped.

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Magnetic Field Structure

• The whole magnetic field is called the
  magnetosphere.
• On the side closest to the sun, where the solar
  wind compresses the field, there is a bow
  shock, just like a boat pushes some water out of
  the way at its bow as it sails forward.

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Why do we care?

• Earths magnetic field isnt just there with no
  purpose. Without it, you and I and every living
  thing on this planet would be dead (including the
  cockroaches!)
• The magnetic field channels away the solar wind.
• It also prevents erosion of the atmosphere.

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Solar Wind

• So what is the solar wind anyway?
• Its radiation extremely hot, high-energy,
  fast-moving charged particles (ions) given off by
  the sun. Most of these particles are protons.
• If you were exposed to it for just a few hours
  without protection, your skin and every organ in
  your body would be burned, and youd have a fatal
  dose of radiation poisoning.

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How does the magnetic field protect us?

• The magnetic field captures the solar wind and
  channels much of it into a donut of radiation
  around the earth.
• This donut (actually 2 layers one inside the
  other) is called the Van Allen Radiation Belt
  (V.A.R.B.)

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Van Allen Radiation Belts

• Satellites must orbit either below or above the
  V.A.R.B., or their electronics would be fried.
• The problem is even worse when we send manned
  missions into space. The ship must pass through
  the radiation belts as quickly as possible or the
  crew is toast !

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Where does the radiation go?

• Since the sun continually supplies new solar
  wind, where does the solar wind go that the earth
  has already captured?
• The magnetic field channels some of it into our
  atmosphere at the north south poles. Here it
  ionizes oxygen and nitrogen atoms, causing the
  beautiful northern and southern lights.

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Northern Lights?

• The northern lights are properly called the
  aurora borealis. Theyre nothing more than a
  very large fluorescent light display (without the
  fluorescent tube!)
• The northern lights are sometimes seen as far
  south as Florida, especially when the sun is very
  active.

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This aurora was photographed in Tennessee in
October, 2002.
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Where does the rest of the radiation go?

• Much of it flows through the magnetic field,
  around the earth, and drips off the tail of the
  magnetic field. The tail is called the
  magnetotail.
• Without our Teflon-coating of magnetic field,
  the earth would have been cooked many billions of
  years ago.

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Switch Gears!

• Lets switch topics, from the magnetic field to
  the atmosphere.
• Earths atmosphere is unlike any other planets
  in chemical composition, but it is like every
  other planets in the processes that go on within
  it.

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Chemical Composition

• Our current atmosphere is
• 78 nitrogen (N)
• 21 oxygen (O)
• 1 argon (Ar), helium (He), carbon dioxide (CO2),
  water vapor (H2O), and about 20 other rare gases.

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Chemical Composition

• The of water in the atmosphere can vary from
  near 0 over deserts to 0.5 in the tropics.
• The of carbon dioxide has doubled in the past
  300 years, from 150 parts per million (ppm) to
  about 340 ppm today.
• This means that our atmosphere is evolving!
  Could it have evolved in the past?

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Atmospheric Pressure

• Pressure is the downward push of the column of
  air above you.
• At earths surface, the air (barometric) pressure
  is 14.7 pounds / square inch.
• Other units are 29.92 inches of mercury in a
  barometer, and 1013 millibars.

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The Atmospheres Structure

• Earths atmosphere has both vertical and
  horizontal structure.
• Vertically, the atmosphere is divided into 4
  layers.
• Horizontally, the atmosphere is divided into 6
  circulation cells, 3 in the northern hemisphere
  3 in the southern.

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4 Layers

• Troposphere, the weather layer. From the earths
  surface to 10 km up. It gets colder the higher
  up you go within this layer.
• Stratosphere, the circulation layer. The jet
  stream and ozone layer that protects us from UV
  light are in this layer. Extends from 10 to 40
  km up. Temperature rises as you go up within
  this layer.

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4 Layers continued

• Mesosphere, a middle layer, up to 75 km. Here
  the air pressure is only 1/10,000th of the
  pressure at the earths surface. The temperature
  again falls as you go up within this
  layer.Thermosphere, the hot layer, up to 120 km.
  This is the outer edge of earths atmosphere.
  Here, the temperature equalizes with the
  temperature of the hot solar wind. This is where
  auroras form.

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What setsoff onelayer fromthe nextis the
waythetemperaturevarieswithin it.
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How does the atmosphere affect the surface?

• in 4 ways
• 35 of the sunlight that hits the atmosphere is
  reflected back into space by clouds.
• The of visible light reflected by a planet is
  called its albedo. Earths albedo is 0.35.
• Clouds, ice, deserts all increase albedo.
• A high albedo generally means that the planet has
  a cold surface (lots of ice.)

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How does the atmosphere affect the surface?

• 33 of the sunlight is absorbed by gases and
  dust, but then is re-radiated as infrared (heat).
  Much of this infrared light goes back into space
  and is lost.
• The absorption of light is called attentuation or
  extinction (just like the dinosaurs!)
• Greenhouse gases (water vapor, carbon dioxide,
  methane or CH4) help to trap the heat and prevent
  it from going back into space.
• Without the greenhouse gases, earths surface
  would be about -18oC.

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How does the atmosphere affect the surface?

• Dust in the atmosphere also causes reddening, a
  process where the blue light is scattered, but
  red light is allowed to pass straight through.
• We see the scattered blue light as the blue of
  our sky. We also see the red of sunset as it
  passes straight through the atmosphere.
• Reddening also happens in space when starlight
  passes through dusty nebulas.
• By the way, only 32 of the sunlight makes it to
  the surface.

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Thereddeningeffect.
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Atmospheric Circulation

• Earths atmosphere has 3 circulation cells in
  each hemisphere (called Hadley cells on other
  planets).
• The northern-most is the polar cell, from 90o to
  60o north latitude
• We live in the temperate cell, from 60o to 30o
  north latitude.
• The southern-most is the tropical cell, from 30o
  north to the equator.

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Atmospheric Circulation

• How does the air circulate?
• Warm air rises at the equator, cools off at high
  altitude, then falls back to the surface at 30o
  north latitude. It eventually circulates back to
  equator.
• The polar cell operates by cold air falling at
  the north pole, flowing away from the pole,
  warming and rising at about 60o north latitude.
• The temperate circulation cell is just caught in
  the middle between the tropical polar cells.

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Atmospheric Circulation

• If the earth didnt rotate, the air in the
  circulation cells would simply move north and
  south.
• However, the earths rotation causes the Coriolis
  Effect. This causes moving wind to turn or
  deflect to the right in the northern hemisphere.
  The circulation cells turn into tubes, allowing
  the winds to move all the way around the globe.

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Click here for an animationof the Coriolis Effect
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Other Planets

• How are other planets atmospheres different?
  Other planets rotate faster or slower, are hotter
  or cooler.
• How would rotating faster affect the atmosphere?
  It might turn circulation cells into bands, where
  the winds simply move from west to east or east
  to west.
• Hotter temperatures could be expected to make the
  wind speeds higher.

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East west bands of winds result from a very
rapid rate of rotation.
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Where did the atmosphere come from?

• Some water and gases were contributed by comets,
  meteors, and other planetissimals impacting on
  earths surface.

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Where did the atmosphere come from?

• But most of the atmosphere came from volcanic
  outgassing. Volcanoes release over 100 billion
  kilograms of water vapor and gases into the
  atmosphere every year.
• Over 4.5 billion years, 5 x 1020 kilograms of
  water and gases have been released. This is
  enough for the atmosphere and the oceans!

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Did the atmosphere change?

• Earth has had 3 atmospheres.
• The first atmosphere was hydrogen (H) and helium
  (He) from the original solar nebula.
• Since these gases are light and the earth was hot
  way back then, most of the H and He was
  eventually lost to space.

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2nd atmosphere

• After the H and He escaped into space, only the
  gases that were too heavy to be lost were left
  behind nitrogen (N2) and carbon dioxide (CO2).
• We still have the N2 today, but where did the CO2
  go?
• Most of it dissolved in the oceans, combined with
  calcium (Ca) and was turned into limestone. Some
  was absorbed by photosynthetic bacteria.

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The layer of limestone belowformed by the
chemical equation CO2 CaO CaCO3
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3rd atmosphere

• As the photosynthetic bacteria began to use the
  CO2, it began to produce oxygen (O2).
• Some of the bacteria evolved into photosynthetic
  plants which increased the rate of O2 production.
• Our present atmosphere is N2 and O2 in about a
  41 ratio.

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First came the photosynthetic bacteria,then the
green plants. Both added oxygen (O2) to our
atmosphere.
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Earths Geology

• Earths surface changes by processes that are
  similar to some of the other planets
• Wind blows particles that cause erosion and build
  up structures like sand dunes and dust fields.
• Flowing water cuts canyons and river beds, and
  transports material. Flood can erode huge
  channels.
• Flowing ice or lava can act much like flowing
  water.
• Subsurface movements cause hills, mountains,
  volcanoes, huge cracks and rift valleys.

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Earths Geology

• Earth also has larger-scale processes that other
  planets dont have plate tectonics.
• Earths crust is divided up into about 20 large
  pieces or plates of rigid crust that float on top
  of flowing mantle.
• Where these plates come together or pull apart is
  where we get mid-ocean ridges, chains of
  volcanoes and mountains, and earthquakes.

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Earths Geology

• The movement of plates is driven by hot currents
  of magma welling up from deep within the mantle
  of the earth.
• Look at the following diagrams closely. Look
  especially for places where the plates are
  separating or crushing together, because well be
  looking for similar features on other planets too!

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A plume of hot magma is welling up from the deep
mantle. Notice how it pushes up the crust. A
mid-ocean ridge may form here.
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The next time you think of the earth, remember
all of the parts that make it up. Well use
this information again, when we start looking
at the other planets!
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Photo Audio Credits

• NASA
• U.S. Geological Survey
• Donald E. Davis NASA
• Cornell University
• B. Tissue