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Earth The Model Planet If you encountered another planet, what would you want to learn about it? Basic physical parameters How old is the planet? – PowerPoint PPT presentation

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Title: Earth

  • The Model Planet

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?

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

Learning more (2)
  • Has the atmosphere always been the same as it is
    now? How has the atmosphere interacted with the
  • What kinds of physical processes have produced
    the planets landforms?
  • Is there life on the planet? How does it
    interact with the various ecosystems?

Physical Properties
Diameter 12,756 km at the equator
Why specify at the equator?
Because the polar diameter is only 12,697 km
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.
Physical Properties
  • Volume 1.1 trillion cubic kilometers (km3)
  • Mass 5.97 x 1024 kilograms

Mt. Everest is about than 2400 km3 http//experts.
This is equal to about 81 moons!
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

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

Physical Properties
  • The density of an object reflects its
  • What does Earths density tell you about its

Earth must be made of a combination of rocks and
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.

How was the earth formed?
  • Accretion
  • Differentiation
  • Interior Structure
  • Evidence, or How sure are we?

  • A rotating cloud of gas dust
  • a nebula

  • Rotation causes the nebula to flatten

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

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

  • 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).

  • 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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  • 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.

  • 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.

Molten Earth, heated by impacts
radioactive decay.
Differentiated (layered) Earth after cooling.
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
  • Mantle
  • Asthenosphere
  • Lithosphere
  • Crust

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,
Interior section of mantle is a thick fluid
called the asthenosphere. The outer mantle the
crust are rigid and are collectively called the
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.)

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
  • Earthquake waves

Earthquake Waves
  • When an earthquake occurs it produces 2 types of
  • 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.

Cornell Univ.
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

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?

Earths Magnetic Field
  • Magnetic fields are made wherever there is an
    electric current, that is the movement of
  • 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

Earths Magnetic Field
  • The electrical currents within the earth cause
    earth to act like a gigantic electromagnetic
  • 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.

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.

Stripes of different magnetic polarity form in
the rocks as the lava from the mid-ocean ridge
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?

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.

Magnetic Field Structure
  • The whole magnetic field is called the
  • 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
  • The magnetic field channels away the solar wind.
  • It also prevents erosion of the atmosphere.

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.

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

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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 !

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.

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

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This aurora was photographed in Tennessee in
October, 2002.
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
  • Without our Teflon-coating of magnetic field,
    the earth would have been cooked many billions of
    years ago.

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

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.

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?

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
  • Horizontally, the atmosphere is divided into 6
    circulation cells, 3 in the northern hemisphere
    3 in the southern.

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.

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 sets off one layer from the next is the
way the temperature varies within it.
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.

The reddening effect.
Atmospheric Circulation
  • Earths atmosphere has 3 circulation cells in
    each hemisphere (called Hadley cells on other
  • 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.

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
  • 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
  • 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.

Click here for an animation of the Coriolis Effect
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.

East west bands of winds result from a very
rapid rate of rotation.
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.

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
  • Most of it dissolved in the oceans, combined with
    calcium (Ca) and was turned into limestone. Some
    was absorbed by photosynthetic bacteria.

The layer of limestone below formed by the
chemical equation CO2 CaO CaCO3
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.

First came the photosynthetic bacteria, then the
green plants. Both added oxygen (O2) to our
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
  • Flowing ice or lava can act much like flowing
  • Subsurface movements cause hills, mountains,
    volcanoes, huge cracks and rift valleys.

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!

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!
Photo Audio Credits
  • NASA
  • U.S. Geological Survey
  • Donald E. Davis NASA
  • Cornell University
  • B. Tissue