Download The habitability of Earth

The habitability of Earth
Tuesday, September 24, 2013
Outline of today’s class
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To learn about the history of life on Earth, we need to
learn the history of the Earth.
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What makes the Earth suitable for life?
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Water + organics + stability.
Volcanism, magnetic fields, plate tectonics: geological activity.
Atmosphere
The question becomes ‘should we be looking for geologically
active worlds in the Solar System?’
Tuesday, September 24, 2013
Worlds in the inner Solar System
Tuesday, September 24, 2013
What Makes the Earth Habitable?
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Distance of Earth from
Sun (not too close, not too
far)
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Liquid water
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Surface gravity
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Atmosphere
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Magnetic field
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Solid surface
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Building blocks of life
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Climate suitable for life
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Plate tectonics
Tuesday, September 24, 2013
The Rock Cycle
Tuesday, September 24, 2013
Strata in Sedimentary Rocks
Tuesday, September 24, 2013
Strata on Mars
Tuesday, September 24, 2013
Endurance Crater on Mars:
photo by Opportunity Rover
Grand Canyon Strata
Tuesday, September 24, 2013
Example on Mars:
you can get relative ages easily
(e.g., mountains, plain, meteor impact)
Tuesday, September 24, 2013
Atomic Numbers, Isotopes, etc.
Tuesday, September 24, 2013
Radioactive Decay
Tuesday, September 24, 2013
Half-life
Tuesday, September 24, 2013
Fossils in Rocks (aged) allow us to study
development of life through geologic ages
Tuesday, September 24, 2013
The Geological time scale
Tuesday, September 24, 2013
Review Questions
Chapter 4 (p147) : Discuss if these statements make sense.
Q23. The most common type of rock in the Grand Canyon is sedimentary.
Q25. If you had a time machine that dropped you off on Earth during the
Hadeon eon, you’d most likely be killed by a large meteor impact.
Q21. Palentologists will find the fossil remains of almost every human being
who ever lived.
Tuesday, September 24, 2013
How Old is the Earth?
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It must be older than the oldest
minerals found on Earth (4.4 Gyr
old)
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zircon found in Australia
It must be older than the oldest
Moon rocks (4.4 Gyr old)
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the Moon formed after the Earth in
the solar nebula hypothesis (next)
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It must be younger than the
oldest meteorites (4.57 Gyr old)
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Scientists estimate that the
Earth is about 4.54 Gyr old
Tuesday, September 24, 2013
Formation of the Moon
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The Moon is thought to
have formed very soon
after the Earth formed
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within 50-150 Myr
It is thought to have
formed from the collision
of a Mars-sized object
very early on
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same composition & density
as Earth’s crust
thus formed after
differentiation of Earth’s
core (at 50-150 Myr)
Tuesday, September 24, 2013
Heavy bombardment on the Moon
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The surface of the Moon
preserves a record of
ancient impact craters
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The lunar maria exhibit
relatively few craters
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this evidence has been
erased on the Earth
these surfaces are younger,
about 3.0-3.9 Gyr old
Most impacts on Earth
must therefore have
occurred during the
Hadean era
Tuesday, September 24, 2013
Life during the Hadean era
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Radiometric dating of zircons
indicates that Earth’s crust
had already formed 4.5 Gyr
ago
This implies that the Hadean
Earth may have been
habitable at that time
Although frequent impacts
may have sterilized the
Hadean Earth
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sufficiently large impacts could
have vaporized all of Earth’s
oceans!
Tuesday, September 24, 2013
Earth’s Interior
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Once the surface forms,
then the interior of Earth
has several important
effects on the surface
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Volcanoes have built up much
of the atmosphere
Plate tectonics have shaped
the continents
Earth’s magnetic field shields
life from the solar wind
Tuesday, September 24, 2013
Plate Tectonics
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Earth’s surface is broken
up into plates which float
on the mantle and move
around slowly
Movement of these plates
is responsible for
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mountain building
sea floor spreading
earthquakes
volcanic hot spots
subduction
rift valleys
continental drift
Tuesday, September 24, 2013
Plate Tectonics at Work
Tuesday, September 24, 2013
Building Earth’s Atmosphere and Oceans
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Earth’s atmosphere and
oceans were produced by
several mechanisms
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Outgassing (e.g. by volcanoes)
of gases trapped within the
Earth **
Material deposited during
impacts (including ice and
minerals from comets)
Life!
Tuesday, September 24, 2013
The Greenhouse Effect
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Greenhouse gases in the
Earth’s atmosphere make
the Earth considerably
warmer than it would
otherwise be
This is a good thing for
life, since it allows liquid
water to survive on
Earth’s surface
However, by adding
manmade greenhouse
gases, we are now
starting to warm the
atmosphere further
Tuesday, September 24, 2013
The Snowball Effect
Greenhouse warming has not been perfect
e.g., ice ages (longest and deepest were ~2.3 Gyr and
700 Myr ago) occur when Earth’s rotation axis tilt
varies (22 to 25 deg) and depend on continental motions,
making seasons more or less extreme
Tuesday, September 24, 2013
Earth’s Carbon Dioxide Thermostat
Tuesday, September 24, 2013
How to Lose an Atmosphere
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Several mechanisms can
lead to the loss of part or
all of a planetary
atmosphere
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thermal escape (gas
molecules move too fast
compared to gravitational
attraction)
impact-triggered escape
solar wind stripping
Tuesday, September 24, 2013
Movies of Aurorae & Solar Storms!!
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Hi all - here are the links that I would have liked to show
you in class.
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this is amongst the best footage of aurora that I have seen:
http://www.youtube.com/watch?v=WL_-Zz7JDoA
this is amazing footage of solar flares and storms
http://www.youtube.com/watch?v=wFb7OZx2NYo
http://www.youtube.com/watch?v=t3A5C91M17A
Hubble Space Telescope images of aurora on Jupiter
http://www.youtube.com/watch?v=oFsoXjFoKf4
Hubble images of aurora on Saturn
http://www.spacetelescope.org/videos/heic1003d/
And here is a fairly recent article on aurora outside the solar
system! http://www.zmescience.com/space/astrophysics-space/
aurora-outside-solar-system-22012013/
Tuesday, September 24, 2013
What Makes the Earth Habitable?
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The size/mass of Earth
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Earth’s distance from the Sun
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Geologic Activity (Volcanoes, Plate tectonics)
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Impacts: not too many, not too few
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Earth’s magnetic field
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The stabilizing effect of the Moon
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Earth’s atmosphere and greenhouse effect
Tuesday, September 24, 2013
Next week
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Try Chapter 4 review questions
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Qs #1, 5, 6, 8, 9, 10, 15, 16, 20, and 21-30.
example Q15: What are the 3 requirements for a planetary
magnetic fileld and how does the EArth meet these? How does
the magnetic field protect our atmosphere?
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Skim Chapter 5
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Assignment #2 is available on the website.
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Friday class is cancelled.
Tuesday, September 24, 2013