Download Life in the Universe - University of Georgia

Habitability of Earth
and
Long-term Climate Change
ASTR 1420
Lecture #7
Sections 4.4 & 4.5
Formation of Stars and Planets
Animation on the formation of star+planets.
Just to understand following slide a little better.
Detailed information on the planetary system formation will be handled
in later lectures.
Formation & evolution of Earth
Today’s Lecture in a single slide!!
Interior Structure
of the Earth
• Earth’s long-term stability depends
on volcanism, plate tectonics  we
need to know the internal structure!
• How do we know?
Overall density versus surface rock
Gravity probe? Magnetic field?
But, mostly from seismic waves!
1200km
2000km
• Interior structure
o Core : Nickel and Iron. Inner core (solid),
outer core (liquid!)
o Mantle : rocky material (silicate
minerals)
o Crust : lowest-density rock.
3000km
Differentiation
Materials that are separated
according to their densities…
• By the time of the Moon creating impact,
Earth was already differentiated!
• How did it happen so fast?
Earth was molten (or at least nearly molten)
throughout its interior…
• Heat sources of the melting
o Impact heat (i.e., formation heat)
o Potential energy of sinking heavy material
o Radioactive decay energy
All terrestrial worlds in out solar system had
similar melting and differentiating…
Continental Drift
• Continental Drift was
proposed by meteorologist
and geologist Alfred Wegener
in 1912
• The idea was inspired by the
puzzle-like fit of South
America and Africa, indicating
these two continents were
part of a single
“supercontinent” about 200
million years ago
Plate Tectonics : Wilson Cycle
http://www.youtube.com/watch?v=ZLJLFYXp-0Q
Plate Tectonics
Seven major plates
• Internal heat makes hot material expand and rise
while cooler material on top contracts and falls
• Plate tectonics produces and recycles seafloor crust
(that is why the seafloor crust is usually less than 200
million years old). At ocean trenches, the seafloor
crust pushes under the less dense continental crust,
returning the seafloor crust to the mantle and may
cause volcanic eruptions.
At plate
boundaries…
Separating boundary
Colliding boundary
Sliding boundary
Hot Spots
• Sometimes, localized plume of mantle material get uplifted…
Hawaiian islands
Yellow Stone Park
On-going…
• In ~100 Myrs, California will slide northward to Alaska, the Mediterranean
Sea will become mountains, Australia will merge with Antarctica
So, plate-tectonics is cool.
What does it have to do with astrobiology?
 Importance of plate-tectonics will be addressed in terms of “long-term
climate stability” in later slides…
Magnetic field as a shield!
High velocity electrified gas (plasma) blows into the Earth at speed of ~250 miles/second!
http://www.gsfc.nasa.gov/gsfc/spacesci/pictures/20020509imagessu/magneticfield_mpeg.mpg
Cause of Magnetic
Field
Electromagnet
• Requirements for a magnetic field
o Electrically conducting fluid
o Convection
o Rotation of the planet
Magnetic Field
• Charged particles from solar flares interact with earth’s magnetic field and
atoms and molecules in Earth’s atmosphere and produce aurora
Auroras : northern
& southern lights
• Aurora Borealis :
• Aurora Australis :
Aurora in Georgia!
Oct. 29, 2003. Dahlonega, GA
Triggered by a coronal mass ejection (CME)… What’s CME? Google for it.
Other Planets, too!
• Jupiter seen in X-ray (Chandra satellite)
Greenhouse effect
•Greenhouse gases (H2O, CO2, CH4):
effectively “trap” infrared light
•Without the greenhouse effect,
global average temperature of the
Earth would be 30°F!
CO2 Cycle
• On Earth, CO2 content in
the air is regulated by
the Carbon Dioxide Cycle
(the carbonatesilicate
cycle, or the inorganic
carbon cycle) to avoid
runaway Greenhouse
effect
• Carbonate rocks :
limestone, calcite,
dolomite, chalk, …
CO2 in the Earth : atmosphere 1, ocean 60, rocks 170,000
Regulation of Earth’s Climate
• The cycle is about 400,000 years
• The CO2 cycle acts as a thermostat
• For the warm Earth, carbonate minerals forms in the oceans at a more rapid
rate, and takes away more CO2
What global warming? We don’t need to worry about it since the CO2 cycle will take care of it!!
Really??  runaway greenhouse effect!
Ice Ages
• Plate tectonics!!
• Different configuration of continents can
cause a climate change (hundreds of million
years cycle).
• But, cycles of ice ages are much faster!
• Why?
Milankovitch cycles
• Serbian scientist:
o Precession
o Obliquity
o Eccentricity
http://www.youtube.com/watch?v=wLAYRdSnRSI
Snowball Earth
Ice reflects light 90% while
water does so only 5%
Long deep ice ages : 750-580 Myr ago, 2.4-2.2 Gyr ago glaciers all the way to
equator!  putting stresses on life (causing faster evolution)  Cambrian
explosion!!
Earth’s long-term Habitability
• Several Key Factors
o
o
o
o
o
o
Volcanic outgassing  atmosphere
Magnetic field shield  atmosphere
Moderate greenhouse effect
CO2 cycle as a climate regulator
Milankovitch cycles and ice ages
Some extreme cases (snowball Earth and hothouse)
? Should we expect to find plate tectonics and CO2 cycle on other planets?
In summary…
Important Concepts
Important Terms
•
•
•
•
•
•
•
•
•
•
Plate Tectonics
CO2 cycle and climate regulation
Greenhouse effect
Runaway greenhouse effect
Snowball Earth
Core, mantle, crust (+ lithosphere)
Plate tectonics
Milankovitch cycles
Differentiation
Precession, obliquity, eccentricity
Chapter/sections covered in this lecture : 4.4 & 4.5