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Reasons for Seasons (recap)Revolution (around the sun)
Rotation (on its axis)
Earth’s Tilt
Axial parallelism
Sphericity
The Earth’s tiltperpendicular to plane of
equator
Q: do these planes form great circles?
Arctic Circle as viewed from above the plane of the ecliptic
Credit: www.physicalgeography.net
24 hrs day
24 hrs night
the parallel of the Arctic Circle is set by Earth’s tilt
equinox June 21
the circle of illumination divides the earth equally into day and night halves - it forms a great circle-
note that 1/2 of earth is always in the light
March of the Seasons
earthyear.mov
Earth’s Modern Atmosphere
Chapter 3
note: relative size of atmosphere not to scale
The atmos-“spheres”
How much atmosphere is there?
How thick is the atmosphere?The atmosphere is incredibly thin - if Earth were the size of a 12” globe, 99% of its atmosphere would be
about as thick as the paint on this globe!
the total mass of the atmosphere is 5.3x1018 kgBUT mass ocean = 1.4x1021 kg
& mass Earth = 6x1024 kg
The atmosphere is crucial to lifeanalogous to a cellular membrane, regulating
what can enter (such as filtering UV rays)
Cre
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air is a mixture of nitrogen and
oxygen with some trace
gases
What is air?
average density of air is 1.3 kg/m3
Evolution of the Atmospherethe present composition of the atmosphere represents
the net sum of many processes (biological and chemical) operating over 100’s of millions of years
if Earth were lifeless, its atmospheric composition
would be very different (for example, no oxygen)
*Probable early atmosphere: CH4, H2, H2O, NH3
*Early Evolution H2 is lost H2O photochemically disassociates H2 is lost CH4 + O2 CO2 + H2O NH3 + O2 N2 + H2O CO2 reacts to form CaCO 3
*3.5 by: N2, CO2, H2O (mostly N2) Photosynthesis and oxygen Fe is oxidized, last banded iron
*2 by to present: evolution of the modern atmosphere
Earth’s atmosphere in the distant past
Stomatapores on leafs
Troughton and Donaldson 1972
atmospheric oxygen (O2) is produced by photosynthesis
6CO2 + 12H2O C6H12O6 + 6H2O + 6O2light
CO2
O2
From World Book © 2002 World Book, Inc., 233 N. Michigan Avenue, Suite 2000, Chicago, IL 60601. All rights reserved. World Book illustration by James Teason
carbon dioxide + light => sugars + oxygen
phytoplankton in oceans
www.ekologija.net/ zajednicki/phytoplankton.jpg
most atmospheric nitrogen (N2) is produced by volcanoes
the other relatively abundant gas, argon (Ar), is inert (not reactive)
and not involved in biological processes
- produced by radioactive decay of 40K
atmospheric carbon dioxide (CO2) is produced and released by terrestrial photosynthesis and
respiration, as well as air-sea gas exchange
atmospheric water vapor (H2O) varies tremendously (from <1 - 4%
by volume) and is affected by evaporation and condensation
air density decreases with height in the atmosphere because of gravity
pressure decreases rapidly with altitude
Credit: http://www.physicalgeography.net
elevation of Mt. Everest
~30% of sea level
elevation where jets typically fly
~20% of sea level
average tropopause elevation
~10% of sea level
the atmosphere has several layers
with distinct properties and
functions
think of these layers as
concentric shells orsphereswe can
characterize vertical profiles
according to three criteria
Troposphere
StratosphereTropopause
over 99% of the atmosphere is contained in the troposphere and
stratosphere
Layers classified by temperature
the tropopause elevation (and thus the thickness of the troposphere) varies with latitude
the tropical tropopause is twice as high as the polar tropopause because of vigorous
surface heating at low latitudes
Cre
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90% of atmospheric
mass ~5x10^18
kg
why does T decrease
with height in troposphere?
why does T increase with height in the stratosphere
?
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