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How atmospheres are created
1.
2.
3.
4.
Direct capture from solar nebula
Outgassing
Evaporation/sublimation
Bombardment– meteors/solar wind
How atmospheric gasses are lost
1.
2.
3.
4.
5.
Thermal escape
Stripping via solar wind/cosmic rays
Atmospheric cratering
Condensation
Chemical reactions
Thermal escape
1. Escape velocity
2. Temperature
3. The mass of the gas particles
The Moon’s atmosphere
Because the Moon has no global magnetic field,
solar wind particles constantly strike the daylight
side of the Moon, causing bits of the surface to
fly off. These particles can travel 10’s of
kilometers and come to rest when they get to
the night side of the Moon.
The Moon may contain a large
deposit of frozen water
The deepest excavation on the Moon is the
Aitken basin which is over 12 km deep and lies
near the south pole. Because the Sun never
shines in this basin it remains perpetually cold
and may contain 6 billion tons of ice, delivered
from impacts with comets.
Mercury’s atmosphere
Mercury is too hot and has too little surface
gravity to hold much of an atmosphere. But
there are trace amounts of oxygen, sodium,
and helium. These must be constantly
replenished.
Mercury
Moon
Discussion
What does the clumpy nature of Mercury’s
atmosphere tell you about its origin?
Mercury may also contain water
ice?
Mercury has radar bright areas near the poles
which are very similar to reflections from
Jupiter’s moons and the polar ice caps on Mars.
Mercury’s rotation axis is nearly perpendicular
to its orbit. Thus within 6.5 degrees of the
poles, crater floors are deep enough that the
Sun never shines there allowing temperatures to
stay below freezing.
Because some of the atmosphere is
constantly escaping into space, atmospheres
have no edge. They just get thinner and
thinner.
Discussion
Can the Earth hold hydrogen and helium gas
in its atmosphere? Explain how you know?
Discussion
Is it possible that any of the other terrestrial
planets or the Moon can hold hydrogen or
helium gas in their atmospheres? Explain why.
Early atmospheres
All of the planets started out with
atmospheres captured directly from the
solar nebula containing primarily hydrogen
and helium.
Early H and He atmsphere lost into space
by thermal escape.
Each of the terrestrial planets then
acquired an atmosphere through a
combination of bombardment and
volcanic outgassing.
In the case of Mercury and the Moon, this
atmosphere was also lost into space over
time.
Discussion
If the terrestrial planets’ atmospheres
came from volcanic outgassing, why is
Earth’s so different from the atmospheres
of Venus and Mars? Where did all the
nitrogen and oxygen in Earth’s atmosphere
come from?
The origin of life on Earth
The oldest surviving rocks on Earth date from 3.8
billion years ago and show that life in the form of
blue-green bacteria already existed on Earth.
These bacteria used photosynthesis to convert
CO2 into O2.
Chemical reactions remove O2
from atmosphere
Bacteria extract oxygen from nitrates in the soil
and emits N2 into atmosphere. N2 is combined
with O2 by lightning to form nitrogen oxides.
The nitrogen oxides are then absorbed by rain
water and re-deposited in the soil.
Oxygen buildup
Approximately 2 billion years ago, oxygen could
no longer be absorbed chemically and started to
build up in atmosphere.
Structure of Earth’s atmosphere
Discussion
Suppose you are on a rotating merry-goround sitting near the center and you
roll a ball toward the edge. Describe
how the ball moves on the merry-goround as it rolls outward.
If you sat at the outer edge and rolled
the ball toward the center how would it
move?
The Coriolis Effect
Discussion
How does the rotation of Venus differ from
that of the Earth?
How would you expect the circulation of
heat to differ on Venus?
Hadley cells on Venus
It “snows” on Venus
The tops of high mountains on Venus are
coated with a shiny substance, much like
high peaks on Earth covered with snow.
On Venus, which is too hot for water snow,
it “snows” lead and magnesium sulfides
which collect on high mountain peaks
which are cooler than the surface.
Discussion
In general, temperature falls with height.
Why does the temperature rise in Earth’s
stratosphere and thermosphere?
Discussion
Why doesn’t the temperature rise in the
stratosphere of Venus, (or more precisely why
doesn’t Venus have a stratosphere)?
Discussion
Why are the pictures from Verona 13 red?
Discussion
Why is Venus so hot? Although Venus is closer
to the Sun than Earth, its cloud cover reflects
nearly 60% of the light that falls on it. The
surface therefore receives less energy from the
Sun that the Earth’s surface does.
The greenhouse effect
Carbon dioxide (as well as water vapor and
methane) absorb infrared radiation. Sunlight can
pass to the surface of Venus and heat it. But the
infrared radiation it emits can not escape back
into space.
Greenhouse temperature
increase
Venus – 400 degrees C.
Earth – 36 degrees C
Mars – 6 degrees C
Tan is opaque White is transparent
Discussion
Explain why the previous plot looks the way
it does.
Discussion
Venus is too hot to have liquid water on the
surface.
Earth has just the right temperature to
liquid water.
Mars is too cold to have liquid water.
Explain why.
The carbon-silicate cycle
Rain water dissolves carbon dioxide, and sulfur
dioxide, forming carbonic acid and sulfuric acid.
This acid rain erodes rocks that contain calciumsilicate minerals.
Carbonic acid reacts with the rock and forms
calcium and bicarbonate ions, which are carried
into the oceans. There these ions are deposited
on the sea floor as limestone or used by plankton
and other organisms for calcium carbonate shells,
which are deposited on the ocean floor when the
organisms die.
Discussion
What happens to the limestone on the
ocean floor? Does it just stay there for the
rest of eternity?
Spreading of the sea floor causes these
deposits to be cycled into the Earth’s
interior where it reacts with quartz to
produce new silicate rock and carbon
dioxide.
Discussion
What would happen if the Earth grew colder
so that the oceans completely froze over?
Discussion
What happens as the average global
temperature of the Earth goes up?
The faint Sun problem
Sun was only 70% as bright as it is today, but
liquid water still existed on Earth
As the Sun brightened, CO2 removed from
atmosphere to regulate temperature.
Discussion
Why is the Sun getting brighter over time?