Transcript A Brief History of Planetary Science

Earth
Astronomy 311
Professor Lee Carkner
Lecture 12
Terra -- The Earth Goddess
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Earth Facts
Size: 12700 km diameter
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Orbit:
Description:
Earth’s Celestial Motions
Earth is tilted on its axis by 23 1/2
degrees
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Earth has large satellite, The Moon
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May stabilize tilt of axis
Earth’s Atmosphere
Composition:
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Very different from other atmospheres
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Early Atmosphere
Where did the original atmosphere come
from?
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Early composition:
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Formation of Atmosphere
Start with CO2, H2O, CH4, NH3
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C, H, O form H2O, CO2
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Final atmosphere -- O2 and N2
Earth’s Atmosphere
Atmosphere and Temperature
Planets with no atmosphere have a
temperature determined by radiation balance:
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For a steady temperature, both rates must be
equal
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K stands for Kelvin, a temperature scale
where 0 K is absolute zero
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To convert K to F:
TF = 1.8TK - 460
The Habitable Zone
In order to support life a planet must be in the
habitable zone
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Width of zone determined by the effectiveness of
the carbonate-silicate cycle
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For our solar system habitable zone width is about
0.95-1.37 AU
Too hot,
water is destroyed
can’t remove CO2
Too cold,
try to warm up
with more CO2
but CO2 forms
clouds and blocks
sunlight
Just right,
temperature
kept stable
at ~273 K
(water is liquid)
Hypothetical Habitable Zone
Why is the Earth Habitable?
It has the right temperature for liquid
water (~273 K) because:
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Not too close or too far from the Sun
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Climate
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Two basic sources of convection
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The Earth’s rotation breaks the atmosphere
up into convection cells that keep the air
circulating, producing global weather
patterns
The Earth’s Surface
What shapes the Earth’s surface?
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Also, volcanoes and cratering
Resurfacing is cyclical and constant
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Unlike other planets the Earth does not have
many craters
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Plate Tectonics
The two top layers of the Earth are the crust
and the mantle
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Crust is broken up into plates that float on the
upper mantle
Plates move around and crash into each other
forming trenches and mountains
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How Plate Tectonics Work
Plate Boundaries
Water
The Earth has more liquid water on its
surface than any other planet
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Water is present on Earth in all three
phases (ice, liquid water, vapor) and
continuously cycles between them
Water on the Earth
Plate Collision -- The Himalayas
The Grand Canyon
Meteor Crater
The Earth’s Interior
The crust and atmosphere are very thin
compared the rest of the planet (like the
skin of an orange)
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We learn about them by studying the
seismic waves from earthquakes
Seismic Waves
Types of waves:
P waves:
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S waves:
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The different densities of the inner earth
refract the waves
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When an earthquake occurs we can measure
the strength of S and P waves all over the
Earth
Earthquake Studies of the
Earth’s Interior
Seismic Waves and the Earth’s
Interior
No S waves detected on opposite side of Earth
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There is a shadow zone where no P or S waves are
detected
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Very faint P waves detected in shadow zone
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Structure of the Earth
Structure of the Earth
Crust:
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Mantle
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Outer core
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Inner core
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 Density increases toward the center
Summary
Earth is unique for at least two reasons
Large amounts of liquid water
constantly reshapes the surface
Large amounts of free oxygen
produced by life
Earth has liquid water and life because
it is in the habitable zone
Summary: Atmosphere
Earth’s initial atmosphere composed of
CHON
H and O form water -- oceans
C and O form carbon dioxide -- rock
N stays in atmosphere
Plants produce oxygen
Mild temperature maintained by
carbonate-silicate cycle
Summary: Surface
Solid iron inner core, liquid iron outer
core, solid mantle and crust
Crust is broken up into plates which
slide around on the upper mantle
Plate tectonics and erosion constantly
alter surface