The Earth Moon System

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The Earth Moon System

• Formation, Development, and Current State

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We were wrong

• It was once believed that Earth was created,
  instantly, 6000 years ago.
• Ancient thinkers like Aristotle and Leonardo da
  Vinci saw fossils as evidence the Earth was much
  older.
• Lord Kelvin used heat to determine an age of
  24-400 million years old
• Arthur Holmes was the first to get a near
  accurate age of the Earth using, determining the
  earth to be about 1.6byo using radioactive decay.
• Later, improved methods of radiometric dating led
  to a much more accurate age of the Earth.

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Formation

• About 4.5 billion years ago, Earth, along with
  the other planets in our solar system began to
  take shape.
• They formed in accretion disks.
• The material that formed the Earth was created in
  supernovas.

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Proto-Earth

• Within 10-20 million years Earth, slightly
  smaller than today, had formed from the accretion
  disk located about 150,000,000km from the sun.
• It is hypothesized that another, even smaller
  planet was also forming at about the same
  distance.
• This planet, Theia, was about the size of Mars.

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Giant Impact Hypothesis

• Shortly after the formation of these two planets,
  Theia struck Earth with a glancing blow.
• This impact liquefied Earth and ejected a large
  amount of molten material.
• The ejected material formed the Moon.
• The remainder of Theia sunk to the center of
  Earth to help form its iron core.
• http//upload.wikimedia.org/wikipedia/commons/d/d1
  /Big_Slash.gif
• There are some other, less likely ideas as to
  how the Moon formed

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Co-Formation Hypothesis

• Before, we visited the Moon and were able to
  analyze its contents, it was thought that the
  Moon formed at the same time and location as
  Earth.
• This would have left the Moon rotating directly
  above the equator with much more Iron than it
  currently has.

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Fission Hypothesis

• It was also once believed that centrifugal forces
  pulled a chunk of earth out into space leaving a
  basin behind which later formed the Pacific
  Ocean.
• This would have required the Earth to be spinning
  much faster than it does today.
• It also would have formed the Moon rotating
  directly above the Equator.
• These facts make this an unlikely hypothesis.

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Capture Hypothesis

• Because the Moons orbit is not directly above
  the equator, it was once believed that the moon
  was formed elsewhere in the Solar System and
  later captured by Earths gravity.
• For this to have occurred the Earth would have
  needed a much larger atmosphere to slow down the
  approaching Moon.
• This too is very unlikely.

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Explanation

• The Giant impact Hypothesis is the most likely
  because it helps explain other features about the
  Earth Moon system.
• Large amount of Iron in the core
• Still molten mantle
• Tilt of the Earth
• Speed of Rotation of Earth

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A Changing Planet Time Line

• 4.5 bya - Magma Earth
• 4.4bya - Ocean Earth
• Carbon dioxide atmosphere, iron rich oceans
• 3.4bya - Continents form
• Granite floats on magma
• 2.2-1.5bya - Blue Planet
• Stromatolites release oxygen that turns oceans
  and sky blue.

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Time Line (cont)

• 1.0bya Rodinia
• Super-continent
• Trilobites best evidence
• 700mya Snowball Earth
• Caused by massive super-continent
• 630mya Cambrian Explosion
• Shallow seas allows for evolution of a wide
  variety of life
• Evidence found in Burgess Shale

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Time Line (cont)

• 300mya - Animals/Plants moved on land
• Oxygen in atmosphere created ozone that protected
  animals and plants from UV rays
• 250mya - Massive volcanic eruptions
• Led to extinction of 95 of living things
• Creation of Pangea
• 235mya - Dinosaurs began to rule
• Lukewarm blooded, allowed them to survive in
  hot, oxygen rich environment.

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Time Line (cont)

• 180mya - Pangea breaks up.
• Dinosaurs survive
• 65mya - KT Boundary
• Asteroid/Comet impacts Mexico
• Volcanoes erupting in India
• Most dinosaurs go extinct

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Time Line (cont)

• 50mya - Mammals began to flourish
• Uplift and Erosion shape surface of Earth
• 2mya - Human ancestors leave Africa
• Ice Ages send glaciers back and forth across the
  continents
• 10,000ya - Last Ice Age retreats
• Human civilization begins

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The Future

• 15000y - New Ice Age
• Within the next 15000 years a new Ice Age will
  begin.
• 200my - New Super-Continent forms
• 2by - Mantle and Core cool
• Stops tectonic movement
• Stops magnetic field

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Earth

• Earth is the 5th largest planet.
• 12,800km diameter.
• Not a perfect sphere
• Centrifugal force makes the circumference around
  equator bigger than circumference around poles.
  (difference of 67km)
• Oblique Spheroid

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Earths Axis

• Earths axis is an imaginary line that runs
  through the Geographic North and South Poles.
• The Earth spins about this axis once every
  23hours 56minutes.
• The axis is tilted at an angle of 23.5º from
  vertical.
• This tilt is responsible for the seasons.

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Seasons

• The seasons have differing weather patterns for
  two reasons
• 1. The angle of the Suns rays varies from most
  direct in the summer (hotter) to least direct in
  the winter (cooler)
• 2. The length of day varies from longest in the
  summer to shortest in the winter, giving the
  Suns rays less time to warm the Earth.
• The Northern and Southern Hemispheres have
  opposite seasons.

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Solstices

• The solstices occur on when the amount of
  daylight is the greatest or least and the angle
  of the Suns Rays are the most or least direct.
• Winter Solstice - December 21st
• Summer Solstice - June 21st

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Equinoxes

• An equinox occurs when there is exactly 12hours
  of daylight and the Suns rays are pointing
  directly at the equator.
• Spring Equinox - March 21st
• Fall Equinox - September 23rd

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Earths Structure

• Earth is comprised of several layers.
• These layers are separated due to their density.
• Crust
• Upper Mantle
• Lower Mantle
• Outer Core
• Inner Core

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Crust

• The Crust is the layer of the Earth we all walk
  on.
• 0-35km below the surface of the Earth.
• Two different types
• Granite Crust - Covers continents, thicker
• Basaltic Crust - Ocean Floor, thinner
• Crust contains rock in all phases of the rock
  cycle.

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Mantle

• The Mantle is the area of rock between the core
  and the crust. (35-3000km)
• The rock is plastic in characteristic and flows
  too slowly to be considered a liquid.
• The difference between the upper and lower mantle
  is due to the way seismic vibrations pass
  through.
• Seems to be pressure related.

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Outer Core

• Liquid layer of Iron and Nickel located between
  the inner core and the lower mantle.
• 3000-5000km deep
• Predominantly responsible for Earths magnetic
  field due to the rapid movement of the liquid
  metal.

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Inner Core

• The center of the Earth.
• Solid alloy of nickel and iron.
• 5000-6400km deep
• Thought to be hotter than the surface of the sun.
  (Remains solid due to immense pressure)

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Earths Magnetic Field

• As a result of the rapidly spinning liquid metal
  found in the outer core, Earth has a magnetic
  field, similar to a giant bar magnet.
• This magnetic field protects us from harmful rays
  and particles emitted from the sun.

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Magnetic Poles

• Just like a bar magnet, Earth has magnetic north
  and south poles.
• A compass is a small magnet that aligns its self
  to Earths magnetic field, always pointing to the
  North and South Magnetic Poles.
• A compass above either magnetic pole will point
  in random directions.
• These poles do not align with Geographic poles.
• They can move up to 15km a year.

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The Moon

• The Moon is Earths only natural satellite.
• It is the fifth largest moon in the Solar System.
• The Moons orbit ranges from a distance 363,000km
  to 406,000km.
• The moon is about 3500km in diameter
• This gives the moon roughly 1/6th the gravity of
  here on Earth.

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Moon (cont)

• The moon takes 27.3 days to orbit the Earth.
• As the Earth is also moving during this time the
  Moon completes its cycle of phases over a period
  of 29.5 days.

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Structure of the Moon

• Like Earth, the Moon has a crust, mantle and
  core.
• Unlike Earth, only a small portion of the Moons
  core is still liquid.
• The Moon has cooled significantly since it was
  formed.

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Surface of the Moon

• The Moons surface has several important
  features.
• Maria - dark, relatively featureless plains on
  the moon.
• Formed as lava filled depressions left by
  impacts.
• Terre - Lighter colored highlands of the moon
• Mountains exist only around the edges of Maria
  and were not formed by tectonic movement.

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Surface of the Moon (cont)

• Regolith - the soil of the Moon
• Result of many impacts breaking up rock into very
  fine particles.
• Maria has 3-5m of regolith, Terre has 10-20m.
• Impact Craters - form as asteroids, meteors, and
  comets impact the Moon.
• Lack of atmosphere leaves these craters
  undisturbed.

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Motion of the Moon

• If we could view the Earth moon system from above
  the North Pole, the moon would rotate around the
  Earth counterclockwise.
• It also rotates once about its axis, again in a
  counterclockwise motion.

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Tides

• One of the most obvious effects of the
  relationship between the Moon and Earth are
  tides.
• Tides are the result of the gravitational pull of
  the Moon and the Sun on Earths oceans.
• They can cause the level of the ocean to change
  as much as 17 meters depending on the location

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Types

• There are two types of tides.
• Spring tides occur when the Moon, Earth and Sun
  form a straight line.
• These tides are the most extreme, highest and
  lowest.
• Gravity of Sun and Moon work together.
• Neap tides occur when the Moon, Earth, and Sun
  form a right angle.
• These tides have the least variation between high
  and low tide.
• Gravity of Sun and Moon are work against each
  other.

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Sides of the Moon

• Because the Moon rotates exactly once for each
  revolution around the Earth, the same side of the
  Moon always faces the Earth.
• We call this side the Near Side of the Moon.
• The Far Side of the moon is often incorrectly
  called the Dark Side of the Moon.
• The Far Side of the moon has almost no Maria.
• Likely due to lack of tidal forces from Earth.

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Phases of the Moon

• Like any sphere lit by a single source, half of
  the moon is always dark.
• As the Moon spins around Earth, we see varying
  amounts of this lit portion.
• When the amount of the lit Moon we can see each
  night is getting larger the moon is considered to
  be waxing.
• The Moon is considered to be waning as the lit
  portion decreases each night.

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New Moon

• The new moon occurs as the moon is between the
  earth and the sun.
• The new moon is not visible.
• It rises and sets with the sun.

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Waxing Crescent

• Is the phase in between the New Moon and the
  First Quarter
• The edge of the Moon is on the right.
• They rise between sunrise and noon and set
  between sunset and midnight.

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First Quarter

• The First Quarter occurs when the Moon and the
  Sun form a right angle with Earth.
• The curved side of the Moon is on the right.
• Rises at noon and sets at midnight.

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Waxing Gibbous

• Occurs between the First Quarter and the Full
  Moon.
• The more rounded side is on the right.
• Waxing Gibbous moons rise between noon and
  sunset, and set between midnight and dawn.

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Full Moon

• Full Moons occur when the Earth is between the
  Moon and the Sun.
• Full Moons rise at sunset and set at sunrise.
• A Blue Moon occurs when there are two Full Moons
  in one month.

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Waning Gibbous

• The phase between a Full Moon and the Last
  Quarter. Gets a little smaller each night.
• The more rounded side is now on the left.
• Rises between sunset and midnight and sets
  between sunrise and noon.

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Last Quarter

• Last Quarter occur when Moon Earth and Sun form
  right angle.
• The round side of the Moon is on the left.
• Rises at midnight and sets at noon.

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Waning Crescent

• Phase between the Last Quarter and the New Moon.
• Edge of moon on the left
• Rises between midnight and sunrise, sets between
  noon and sunset.

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Eclipses

• An eclipse occurs as the shadow of the Earth or
  Moon blocks the sun from the other.
• Because the Moon revolves around Earth at a
  slight angle, and is quite a distance from Earth,
  rarely does the shadow of one obscure the other.

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Solar Eclipse

• Solar Eclipses occur as the Moon casts a shadow
  on the Earth.
• The Moons shadow has two parts
• Umbra - darker, center part of the shadow
• Penumbra - lighter outer part of the shadow
• An area that lies in the Umbra will see a full
  solar eclipse
• An area that lies in the penumbra will see a
  partial solar eclipse.

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Occurrence

• Must occur during the New Moon phase.
• They occur somewhere on Earth about every 18
  months.
• A total solar eclipse occurs in any given area of
  Earth about once every 370 years.
• As the shadow moves at 1700km/hr totality only
  lasts for at most 7.5 minutes.

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Lunar Eclipse

• A lunar eclipse occurs as the Moon passes through
  the Earths shadow.
• Like solar eclipses, lunar eclipses vary
  according to the part of the shadow that Moon
  passes through.
• As the shadow occurs on the Moon it can be seen
  from the entire hemisphere that can view the
  Moon.
• Because of this Lunar Eclipses are seen more
  frequently

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