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Chapter

Chapter Seven Review: Earth


Department
Astronomy
Course Code
ASTA01H3
Professor
Brian Wilson

Page:
of 10
October 12th, 2010
ASTA01H
Intro to Astronomy and Astro Part I
Chapter Seven: Earth
Overall Structure of Planet Earth
Earth’s mass is 6.0kg
Earth’s radius is about 6400km
oDividing these together, we find that Earth’s average density is 5500
kg/
We can conclude that because the surface layers have densities much less
than average, much denser material must lie deeper
Earth’s interior
oA thick mantle surrounds a smaller, two-part core
oA relatively thin crust, compromising the solid continents and sea floor
oThe hydrosphere, contains the liquid oceans
oAn atmosphere of air just above the surface
oAt much greater altitudes, a zone of charged particles trapped by Earth’s
magnetic field forms the magnetosphere
Earth’s Atmosphere
Mixture of gases:
oNitrogen 78%
oOxygen 21%
oArgon 0.9%
oCarbon Dioxide 0.03%
oWater vapour varies from 0.1 to 3%
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Atmospheric Structure
Troposphere: The portion of the atmosphere below about 12km (weather zone)
Stratosphere: Above the troposphere to an altitude of 40 to 50km
Mesosphere: 50 to 80km from Earth’s surface
Ionosphere: Above about 80km. Where the atmosphere is kept partially ionized by
solar ultraviolet radiation
Atmospheric densities decrease steadily with increasing altitude
The troposphere is the region of Earth’s (or any other planet’s) atmosphere
where convection occurs
Convection: The constant rising of warm air from the Earth’s surface and the
concurrent downward flow of cold air to replace it
At higher altitudes the opposite effect occurs: The air gradually cools,
becoming more denser and therefore sinking back to the ground
These convection cells are responsible for atmospheric heating, as well as surface
winds
Above about 100km, in the ionosphere, the atmosphere is greatly ionized
from the Sun’s radiation spectrum, which breaks molecules into atoms and
atoms into ions
oThe degree of ionization increases with altitude
Atmospheric Ozone
Ozone Layer: At an altitude of around 25km, incoming solar ultraviolet radiation is
absorbed by atmospheric ozone and nitrogen (Ozone = ξ€ˆξ€‡)
oThis solar radiation breaks ozone down, forming oxygen gas again
Ozone is one of many insulating spheres that protect our planet
Surface Heating
The Earth’s surface absorbs much of the solar radiation that is not deflected
by the Earth’s atmosphere
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Eventually the Earth reradiates as much energy back into space as it receives
from the Sun, this stable balance, if uninterrupted, would put Earth’s average
temperature at -23
Solar radiation, which includes a full spectrum of various forms, arrives at the
Earth as sunlight, however some of these radiations forms are blocked or
absorbed by the Earth’s atmosphere
This reemitted energy is in the form of infrared (heat) radiation, which is
partially blocked by Earth’s atmosphere, allowing for a warmer average
temperature as some of the heat is retained within the atmosphere
This partial trapping of solar radiation is known as the greenhouse effect
The magnitude of the greenhouse effect is highly sensitive to the
concentration of greenhouse gases (gases that absorb infrared radiation) in the
atmosphere
oCarbon dioxide and water vapour are the most important of these
Origins of Earth’s Atmosphere
When Earth first formed, any primary atmosphere it might have had would have
consisted of the gases most common in the early solar system:
oHydrogen
oHelium
oMethane
oAmmonia
oWater Vapour
Almost all of this low-density material (especially hydrogen and helium)
escaped into space
Consequently, Earth developed a secondary atmosphere, which consisted of gases
outgassed (expelled) from the planet’s interior from volcanic activity, which include:
oWater Vapour
oMethane
oCarbon Dioxide
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