Planet Earth

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Planet Earth
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How old is the Earth?

1. 140 million years
2. 500 million years
3. 1 billion years
4. 4.6 billion years
5. 13 billion years

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The Early History of the Earth
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Earth formed 4.6 billion years ago from the inner
solar nebula.
Four main stages of evolution
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What is differentiation?

1. The mixing of substances.
2. Lighter substances sinking to the bottom, while
   heavier substances rise to the top.
3. Heavier substances sinking to the bottom, while
   lighter substances rise to the top.
4. The chemical change of substances near the
   surface of a planet due to chemical reactions
   with the atmosphere.
5. The chemical change of substances near the core
   of a planet induced by great heat.

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The Early History of the Earth
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Earth formed 4.6 billion years ago from the inner
solar nebula.
Four main stages of evolution
Two sources of heat in Earths interior

• Potential energy of infalling material

• Decay of radioactive material

Most traces of bombardment (impact craters) now
destroyed by later geological activity
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What killed the dinosaurs (according to the most
widely accepted theory)?

1. Global climate change caused by variations in the
   suns energy output.
2. Global climate change caused by a massive
   meteorite/comet impact.
3. A reptile dysfunction.
4. A nearby stellar explosion (supernova / gamma-ray
   burst).
5. Nothing. They still exist (see, e.g., Jurassic
   Park)!

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Meteorite Impacts on Earth
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Over 150 impact craters found on Earth.
Most famous example Barringer Crater near
Flagstaff, AZ
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Impact Craters on Earth
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Barringer Crater 1.2 km diameter 200 m deep
Formed 50,000 years ago by a meteorite of 80
100 m diameter
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The Chicxulub Crater
Much larger impact features exist on Earth
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Impact of a large body (comet nucleus?) formed a
crater 180 300 km in diameter in the Yucatán
peninsula, 65 million years ago
This impact may have caused major climate change,
leading to the extinction of many species,
including dinosaurs.
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Earths Interior
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Direct exploration of Earths interior (e.g.
drilling) is impossible.
Earth quakes produce seismic waves.
Earths interior can be explored through
seismology
Seismic waves are bent or bounce off transitions
between different materials or different
densities or temperatures.
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If you are standing next to railroad tracks and
you dont see or hear a train, you can tell if
theres a train approaching by putting your ear
on the tracks. This works because

1. your visual abilities improves when you block one
   of your ears.
2. sound waves travel more rapidly along the tracks
   than through the air.
3. Sound waves get less absorbed when traveling
   along the tracks than through the air.
4. All of the above.
5. 2. and 3.

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Earths Interior (II)
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Basic structure
Solid crust (light Si-based materials)
Solid mantle (light elements, iron-poor)
Liquid core (iron-rich)
Solid inner core (iron-rich)
Earths interior gets hotter towards the center.
Earths core is as hot as the suns surface
metals are liquid near the core.
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Earths Magnetic Field
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Earths core consists mostly of iron nickel
(materials that magnets are made out of)
Convective motions and rotation of the core
generate a dipole magnetic field
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The Role of Earths Magnetic Field
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Earths magnetic field protects Earth from
high-energy particles coming from the sun (solar
wind).
Surface of first interaction of solar wind with
Earths magnetic field Bow shock
Region where Earths magnetic field dominates
magnetosphere
Some high-energy particles leak through the
magnetic field and produce a belt of high-energy
particles around Earth The Van Allen belts
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Which phenomenon is caused by the interaction of
energetic particles from the sun with Earths
magnetosphere?

1. Northern lights (aurora borealis).
2. Sun spots.
3. Prominences.
4. Hurricanes.
5. Earthquakes.

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The Aurora (Polar Light)
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As high-energy particles leak into the lower
magnetosphere, they excite molecules near the
Earths magnetic poles, causing the Aurora
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Tectonic Plates
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Earths crust is composed of several distinct
tectonic plates, which are in constant motion
with respect to each other ? Plate tectonics
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Tectonic Plates (II)
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Evidence for plate tectonics can be found on the
ocean floor
and in geologically active regions all around
the Pacific
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Geological activity around the Pacific
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Earthquakes Kobe (Japan)
Volcanism Mt. St. Helen
Volcanism Pinatubo (Philippines)
Earthquakes San Francisco
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The major Tsunami of 2004 in the Indian Ocean was
caused by tectonic activity at the boundary
between

1. the African and the Indian-Australian Plates.
2. the Indian-Australian and Eurasian Plates.
3. the African and the Arabian Plates.
4. the Arabian and the Indian-Australian Plates.
5. the African and Antarctic Plates.

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Plate Tectonics
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Tectonic plates move with respect to each other.
Where plates move toward each other, plates can
be pushed upward and downward ? formation of
mountain ranges, some with volcanic activity,
earthquakes
Where plates move away from each other, molten
lava can rise up from below ? volcanic activity
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Active Zones Resulting from Plate Tectonics
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The interaction between the Pacific and the North
American Plates is responsible for the formation
of

1. the Hawaiian Islands.
2. the Alps.
3. the Rocky Mountains.
4. the Andes.
5. the Appalachian Mountains.

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Volcanism on Earth (I)
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Subduction Zones
Volcanism on Earth is commonly found along
subduction zones (e.g., Rocky Mountains).
Example Stromboli (Sicily, Italy, 1998)
This type of volcanism is not found on Venus or
Mars.
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Hawaii is also very volcanically active. Is this
also because Hawaii is located at a plate
boundary?

1. Yes, it is located at the boundary of the Pacific
   plate.
2. Yes, it is located at the boundary of the North
   American plate.
3. Yes, it is located at the boundary of the
   Eurasian plate.
4. No. This must be a different kind of volcanic
   activity.
5. No. Hawaii is not volcanically active.

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Shield Volcanoes
Volcanism on Earth (II)
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Found above hot spots
Fluid magma chamber, from which lava erupts
repeatedly through surface layers above.
All volcanoes on Venus and Mars are shield
volcanoes
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Shield Volcanoes (II)
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Tectonic plates moving over hot spots producing
shield volcanoes ? Chains of volcanoes
Example The Hawaiian Islands
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Earths Tectonic History
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Earths Tectonic History (II)
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History of Geological Activity
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Surface formations visible today have emerged
only very recently compared to the age of Earth.
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Guess How thick is the Earths breathable
atmosphere (beyond which you would need oxygen
masks to breathe), compared to the Earths radius?

1. 1/24,000 Earth radius.
2. 1/800 Earth radius.
3. 1/15 Earth radius.
4. 1 Earth radius.
5. 10 Earth radii.

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Earths Atmosphere
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Only about 1/800 of the Earths radius!
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Which is the most common gas in Earths
atmosphere?

1. Oxygen
2. Nitrogen
3. Carbon dioxide
4. Methane
5. Water vapor

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The Atmosphere
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Earth had a primeval atmosphere from remaining
gasses captured during formation of Earth
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Do you think that the Earths atmosphere is still
very similar to what it was about 4 billion years
ago?

1. Yes
2. No

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The Atmosphere
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Earth had a primeval atmosphere from remaining
gasses captured during formation of Earth
Atmospheric composition severely altered (?
secondary atmosphere) through a combination of
several processes
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Sources of Atmospheric Gas
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• Outgassing Release of gasses bound in compounds
  in the Earths interior through volcanic activity

• Later bombardment with icy meteoroids and comets

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Loss of Atmospheric Gas
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• Chemical reactions in the oceans

• Energetic radiation from space (in particular,
  UV)

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Which of these processes might be the main reason
that Mercury has almost no atmosphere?

1. Thermal Escape
2. Stripping by energetic radiation from space
3. Condensation
4. Chemical reactions
5. Ejection by impacts

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Which of these forms of radiation from space can
reach the Earth unabsorbed?

1. Radio waves.
2. Infrared light.
3. Ultraviolet light.
4. X-rays.
5. Gamma-rays.

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The Electromagnetic Spectrum
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Wavelength
Frequency
High flying air planes or satellites
Need satellites to observe
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The Interactions between Light and Molecules
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X-rays
1) Splitting up molecules into atoms
2) Ionizing (kicking electrons out of) atoms or
molecules
Nitrogen (N2) / Oxygen (O2)
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The Interactions between Light and Molecules
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Ultraviolet
Splitting up molecules, in particular, Ozone
Ozone (O3)
Oxygen (O2)
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Why is the totally eclipsed moon visible at all
(in a faint red glow)?

1. Because it is still glowing from the intense
   light it received during full moon before the
   eclipse.
2. Because it is illuminated by sunlight reflected
   off other terrestrial planets.
3. Because it is illuminated by sunlight scattered
   within the Earths atmosphere.
4. Because it is very shy during the eclipse and
   turns red when you are looking at it.
5. None of the above The totally eclipsed moon is
   completely black.

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The Interactions between Light and Molecules
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Visible Light
Penetrates through the atmosphere mostly
unabsorbed, but can get scattered
This is why the sun appears red at sunrise and
sunset and why the sky is blue (if its not
cloudy)
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The Interactions between Light and Molecules
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Infrared
Causes asymmetric molecules to rotate
This is the essential step of the Greenhouse
Effect!
Carbon dioxide (CO2) / Water vapor (H2O) / any
other asymmetric molecules (greenhouse gases)
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We know that UV and X-ray radiation from space is
heating the atmosphere. Thus, do you expect that
the atmosphere becomes hotter or colder with
height, very high above the ground?

1. Hotter with increasing height.
2. No temperature change.
3. Colder with increasing height.

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The Temperature Structure of Earths Atmosphere
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Exosphere Heated by UV and X-rays from space
Thermosphere Heated by X-rays from space
Stratosphere Heated by UV radiation from space
Top of Ozone Layer
Ozone Layer
Altitude
Troposphere Heated by greenhouse effect
Temperature
Atmosphere gets colder at larger distance from
heat sources.