Download EARTH DIFFERENTIATES

EARTH DIFFERENTIATES
- EARLY EARTH UNIFORM (HOMOGENEOUS)
- PLANET HEATS UP
- DENSE IRON CORE SINKS, LEAVING LAYERED PLANET:
LIGHT CRUST ON TOP , CORE BELOW, AND MANTLE IN BETWEEN
- DIFFERENTIATION CONTINUES TODAY AS PLANET COOLS
BY THERMAL CONVECTION - PLATE TECTONICS
-HENCE EARTH'S EVOLUTION IS CONTROLLED BY ITS
THERMAL HISTORY- TEMPERATURE AS A FUNCTION OF
DEPTH AND TIME ("HEAT IS THE GEOLOGICAL LIFEBLOOD OF PLANETS")
Press & Siever
HEAT (A FORM OF ENERGY) TRANSFER OCCURS BY
- RADIATION - HEAT TRANSFER BY ELECTROMAGNETIC WAVES
(SUNLIGHT)
IMPORTANT AT EARTH SURFACE BUT NOT VERY
EFFICIENT IN SOLID EARTH
- CONDUCTION - HEAT TRANSFER BY MOLECULES COLLIDING
(TOUCH A HOT OR COLD OBJECT)
IMPORTANT IN SOLID EARTH BUT SLOW
- CONVECTION - HEAT TRANSFER BY MOTION OF MATERIAL
(HOT AIR IS LESS DENSE THAN COLD, SO IT RISES)
IMPORTANT IN SOLID EARTH, OCEAN, AND ATMOSPHERE - MORE
EFFICIENT THAN CONDUCTION
____________________________________________________
ANALOGY: MONEY CAN BE TRANSFERRED ELECTRONICALLY (fast but
easily disrupted), BY MAIL (slow), OR BY CARRYING BAGS OF CURRENCY
IF WE HEAT A PAN OF WATER
FIRST GET SLOW HEAT TRANSFER BY CONDUCTION
LATER, ROLLING BOILING STARTS. FAST HEAT TRANSFER
BY CONVECTION - MORE EFFICIENT
Davidson 2.25
CONVECTION CELL
FLUID HEATED FROM
BOTTOM
HOTTER, LESS
DENSE, FLUID RISES
& COOLS
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COLDER, DENSER
FLUID SINKS &
WARMS
OCCURS BECAUSE
FLUID EXPANDS
WHEN HEATED &
BECOMES LESS
DENSE
Also happens in
stars, ovens anywhere a fluid is
heated!
CRUCIAL FOR UNDERSTANDING ATMOSPHERE
(WEATHER), OCEAN (CURRENTS) & SOLID
EARTH - BOTH IN MANTLE & CORE
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CONVECTION IN ATMOSPHERE
Sun heats earth’s surface
Warm moist air rises, cools, loses
moisture (rain)
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Cool dry air sinks
Makes earth’s climate belts:
wet temperate zone (Chicago)
dry deserts (Arizona, Sahara)
wet tropics (near equator)
Colder in mountains,
airplanes
Davidson 1.15
PLATE TECTONICS AS CONVECTION
Plate tectonics is the surface manifestation of convection cells in earth’s
mantle .
Ridges (spreading centers) mark upwelling, hot limbs.
Trenches (subduction zones) mark cold downwelling limbs.
Oceanic plates form at ridges, cool as they spread and move
across the ocean basins, and heat up as they subduct.
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More
complicated
than simple
pot of water,
but idea’s
the same
EARTH'S HEAT ENGINE TODAY
CONVECTION IN ROCKY MANTLE
CONVECTION IN LIQUID IRON OUTER CORE
SOLID INNER CORE FREEZES FROM LIQUID OUTER CORE
70% HEAT TRANSFER BY PLATE TECTONICS (CONVECTION THROUGH
MANTLE)
25% CONDUCTION THROUGH CONTINENTS
5% (?) BY MANTLE PLUMES
Davidson
2.26
PLATE MOTIONS & PLANETARY EVOLUTION
> Plate motions from continuing
evolution & differentiation from
originally uniform planet to
layered one
> Vertical movement of heat &
material through time
> Lithosphere (plates)- cold
strong outer boundary later of
earth
Plate tectonics causes volcanism, that produces atmospheric
gasses (carbon dioxide CO2 and water H2O) needed to support life
and keep planet warm (“greenhouse effect”)
VOLCANIC
GAS
MAMMOTH LAKES, CA - PART OF
LONG VALLEY CALDERA, ERUPTED
760,000 YEARS AGO - STILL ACTIVE
GAS KILLED TREES, SICKENED
PEOPLE, CLOSED CAMPGROUND
THE EARLY ATMOSPHERE
After Earth formed 4.5 Byr ago,
gases accumulated from
volcanism and comet impacts.
Volcanic gases are very different
than the present atmosphere:
mostly H2O (85%) and CO2 (10%),
with some nitrogen and sulfur.
So the early atmosphere was
probably H2O and CO2 with a bit
of nitrogen. Comets - more
common then – probably
contributed significant H2O.
H2O and CO2 are efficient
greenhouse gases, so 4 Byr
ago the earth was MUCH
hotter than today.
PRIMEVAL ATMOSPHERE EVOLVED TO TODAY’S
1. H2O removed from the atmosphere by precipitation, ending up
in oceans, lakes, etc.
2. CO2 removed by dissolving into rain
> Dissolves into ocean waters
> Reacts with carbon compounds to FORM sedimentary rocks
3. Later (about 2 BYr ago), photosynthesis from plants removed
more CO2 & added oxygen
COMPARED TO ORIGINAL, TODAY'S ATMOSPHERE
>MUCH less dense
>Nitrogen (a trace gas from volcanic eruptions) the most abundant gas
>Oxygen a major constituent (good for us)
PRESENT EARTH'S ATMOSPHERE:
Nitrogen - 78%
Oxygen - 21%
Carbon Dioxide - 0.03%
Argon - 0.9%
Trace Gasses
(Ne, He, krypton, H2, ozone)
Water Vapor - 0% - 4%
Composition persists due to
PLATE TECTONICS (volcanism),
RAIN, & LIFE
Requires temperatures for LIQUID WATER
NOT TOO HOT, NOT TOO COLD
Venus too hot
Mars too cold
PLATE TECTONICS CAUSES VOLCANISM THAT PRODUCES
ATMOSPHERIC GASSES (including carbon dioxide CO2 & water H2O)
THAT SUPPORT LIFE & KEEP PLANET WARM (GREENHOUSE)
NY Times
GREENHOUSE EFFECT
Short wavelength
solar radiation
passes through
glass
Things in
greenhouse absorb
energy, heat up, &
re-readiate longer
wavelengths
Longer
wavelengths can’t
pass through glass
Greenhouse heats
up
Davidson 15.27
GREENHOUSE EFFECT
>Some atmospheric
gasses (including CO2,
H2O, CH4) trap heat
>Earth's surface about
33oC warmer so life can
thrive
Natural greenhouse effect
keeps us alive
Increased greenhouse
gasses due to human
activity
>promote global warming
>likely climate changes in
precipitation, storm
patterns, sea level,
agriculture, etc…
> Some win, some lose
GREENHOUSE
GASSES
ELECTROMAGNETIC SPECTRUM
Incoming
visible light
from sun can
pass through
atmosphere
Water vapor
and CO2
absorb
outgoing
(reradiated)
longer
wavelength
radiation
Planet warms
up
Davidson
15.28
Fraction of light absorbed
GLOBAL WARMING
Estimated changes in annual global mean temperatures and
carbon dioxide concentrations over the past 137 years
relative to a 1961-90 base period.
Temperature data (deg C) go through 1996 (red line)
Carbon dioxide values are from ice cores until 1956 (blue
dashed line) and from air sampling at Mauna Loa, Hawaii from
1957 through 1995 (blue solid line).
9/29/05
Arctic ice melting faster as temperatures rise
Arctic sea ice extent has
dropped to 2.05 million sq.
miles, the lowest in the satellite
record. Trend has various
consequences, some bad,
some good, depending on
Satellite observations show sea ice in the Arctic
melting faster while air temperatures in the region
are rising.
one’s view
Walrus on melting ice basks in the sun in
Chukchi Sea, between Alaska and Russia.
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Glaciers have been retreating rapidly. These are excellent monitors of climate
change
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Melting of West Antarctic and
Greenland ice sheets would raise
sea level 10 or more meters
Red areas along gulf and east
coasts would be flooded,
affecting 25% of US population
If only the Greenland Ice Sheet melts, the impacts will be enormous. Red
areas in this image of southern Florida show effects of a five-meter rise of
sea level. Yellow areas denote urban locations.
Could global
warming start a
little Ice Age?
Heat transported north by warm surface water, released to
atmosphere, keeps climate moderate (Gulf Stream)
Cold, saltier, denser deep water flows south
Melting of northern hemisphere ice sheet and glaciers could release
lots of fresh water, lower density of southward flow, shut down
conveyer
Northern hemisphere would get colder
www.whoi.edu/institutes/images/naocirc.mov
http://movies.yahoo.com/shop?d=hv&cf=trailer&id=1808417410
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COMPARISON OF TERRESTRIAL PLANETS
-ON EARTH DIFFERENTIATION CONTINUES TODAY AS PLANET COOLS
BY THERMAL CONVECTION - PLATE TECTONICS, SO PLANET IS
"GEOLOGICALLY ALIVE"WITH MOUNTAIN BUILDING, EARTHQUAKES,
VOLCANOES, ETC.
-MERCURY AND MARS ARE SMALLER PLANETS THAT LOSE HEAT
FASTER (small cookies cool faster than large ones, small ice cubes melt
faster than big ones, small animals have to eat almost all the time to
keep alive - while big ones can sleep)
-THUS MERCURY AND MARS COOLING HAS GONE SO FAR THAT
THEY HAVE THICK LITHOSPHERE AND ARE "GEOLOGICALLY DEAD”
- NOT CLEAR ABOUT VENUS
- EARTH IS "GEOLOGICALLY YOUNG" - MERCURY AND MARS ARE
"GEOLOGICALLY OLD" - THOUGH THEY FORMED AT THE SAME TIME
(dog years versus human years)
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VENUS - RUNAWAY GREENHOUSE
Dense atmosphere (90 times Earth's)
composed mostly of CO2 (carbon dioxide).
Thick clouds of sulfuric acid obscure the
surface.
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Atmosphere produces run-away greenhouse
effect that raises Venus' surface temperature
to over 450 deg C (hot enough to melt lead).
Venus' surface hotter than Mercury's despite
being nearly twice as far from the Sun.
Venus probably once had lots of water like
Earth that boiled away, leaving it quite dry.
Earth might be like this if it were a little
closer to the Sun.
Not yet clear why Venus turned out so
differently from Earth
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MARS - TOO
COLD & DRY
NOW
VERY THIN
ATMOSPHERE
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MARS - LIQUID WATER IN PASTSHOWN BY LANDFORMS & MINERALS
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MARS CLIMATE CHANGED –
PERHAPS MANY TIMES BETWEEN HOT/WET PERIODS
GREENHOUSE GASSES KEPT
PLANET WARM
WITHOUT ENOUGH GASSES:
SURFACE TOO COLD FOR LIQUID
WATER AND MOST LIFE (if ever
existed)
GOOD PLANETS ARE HARD TO FIND
Venus
HUMAN-TYPE LIFE REQUIRES NARROW
RANGE OF CONDITIONS: TEMPERATURES
(LIQUID WATER) & OXYGEN ATMOSPHERE
SUN, EARTH (PLATE TECTONICS), OCEANS,
ATMOSPHERE, LIFE INTERACT IN
COMPLICATED WAYS TO KEEP EARTH
HABITABLE
Earth
VENUS (TOO HOT), MARS (TOO COLD), &
EARTH (JUST RIGHT)
GOOD PLANETS - AND HENCE
INTELLIGENT LIFE MAY BE RARE
EARTH CLIMATE VULNERABLE TO
CHANGES THAT MIGHT MAKE IT SO HOT
("GREENHOUSE") OR SO COLD
("ICEHOUSE") TO SIGNIFICANTLY IMPACT
CIVILIZATION
Mars
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