conditions for life. mercury earth jupiter uranus venusmarssaturnneptune our solar system
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Conditions for lifeConditions for life
http://photojournal.jpl.nasa.gov
Mercury Earth Jupiter Uranus
Venus Mars Saturn Neptune
Our solar systemOur solar system
Earth, our home
http://visibleearth.nasa.gov
Earth: Earth: Goldilocks ZoneGoldilocks Zone
Earth’s position (“third rock from the Sun”) is in the “Goldilocks Zone” (0.9 – 1.4 AU) that is, in a position that is not too hot and not too cold
(“just right”) Venus is too hot, Mars is too cold, Earth is just
right note: 1 Astronomical Unit (AU) = 149,598,000 km
http://www.dailymail.co.uk
Venus Earth Mars
Distance from Sun
0.72 A.U. 1 A.U. 1.52 A.U.
Mass 4.87 x 1024 kg 5.98 x 1024 kg 6.42 x 1023 kg
Density 5.25 g cm-3 5.52 g cm-3 3.94 g cm-3
Gravity 0.88 Earth gravity
1 Earth gravity 0.38 Earth gravity
Radius 6052 km 6378 km 3397 km
Atmospheric pressure
90.9 atm 1 atm 0.069 atm
Surface temperature
460 C 15 C -59 C
Atmospheric CO2
96% 0.0389% 95%
Atmospheric N2 3.5% 77% 2.7%
Water vapour 0.01% 1% 0.03%
Oxygen 0% 21% 0.13%
Venus
http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-venus.html
http://blog.thomaslaupstad.com/2007/04/12/moon-venus-and-earthshine/
moon
Venus!
http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-mars.html
Mars
Earth, Venus, and MarsEarth, Venus, and Mars
Earth actually has similar composition with Venus and Mars but water is not stable or not present in Venus or Mars
Venus is very hot (460 C) – hot enough to melt lead has a dense atmosphere, mainly composed of CO2
atmosphere is shrouded with clouds of sulfuric acid and water droplets
because of thick cloud cover, Venus surface receives only 44% of solar radiation that Earth does
but heat from surface is nearly completely absorbed by clouds and atmosphere
runaway greenhouse warming
Runaway greenhouse warming in VenusRunaway greenhouse warming in Venus
Venus has no way of removing CO2
Perhaps early in Venus history, Venus had plate tectonics and oceans to control climate
But as the Sun became hotter, ocean boiled away Nearer Sun, hotter. H2O readily evaporates from surface Because of its proximity to the Sun, there is no cold trap
(for water to condense into ice) water vapor rises to high altitudes, where it is more
easily destroyed by solar UV H2O dissociates to H and O. H, being light, escapes, but O reacts with other
molecules to form other molecules means increasingly more water is being lost
Absence of cleansing action by H2O precipitation permits CO2 atmosphere to grow
Absence of water means rock weathering also ceases to capture CO2 from the atmosphere and lock it to form carbonate rocks
CO2 traps infrared radiation from surface => temperature rises => more liquid water evaporates => enhances Greenhouse further this positive (amplifying) feedback produces a
runaway greenhouse effect All water is eventually removed from the atmosphere
yields a massive, very hot, and dry CO2 atmosphere
Continuous volcanic out gassing of materials like sulfur dioxide without water cleansing produces sulfuric acid clouds without its abundant water, Earth would probably be
like Venus Venus is hotter than Earth because of its greenhouse
gases rich atmosphere without these gases, Venus would actually be -20 C
and any water would be frozen hotter than Earth not so much because Venus is
closer to the Sun
… … and the problem with Marsand the problem with Mars
Mars is very cold (-59 C) and has a very thin CO2 atmosphere
Mars may have once had water in a very large northern basin, Oceanus Borealis
Mars is 90% lighter than Earth lower gravity on Mars
means Mars cannot hold onto its early atmosphere Mars is also too small
to have sustained plate tectonics rocks cannot return CO2 into the atmosphere geochemical cycle has stopped
so Mars loses heat easily
Earth’s shieldsEarth’s shields
Earth supports life because it has abundance of water and water exists primarily as liquid (not as vapour or ice)
Earth is also shielded from UV by the ozone layer in the stratosphere
Earth’s magnetic fields shield us from the Sun’s solar wind (flux of electrons, protons, and
charged helium nuclei) that travel several hundreds of kilometers per second
can kill a human cosmic rays (protons and heavier nuclei particles)
travelling at near light speeds rays come from extra solar activities such as
supernova explosions
The water molecule
E.A. Mathez, 2009, Climate Change: The Science of Global Warming and Our Energy Future, Columbia University Press.
WaterWater
WaterWater
2 atoms of hydrogen and 1 atom of oxygen - H2O One of the most unique and most important molecule on
Earth Ice (solid water) has a lower density than liquid water,
so ice floats other molecules: solid phase will sink (higher
density)
O
H H104.5
positive side
negative side
Ice forms at the surface of water ice is now a heat insulator for the waters below below ice is liquid water (crucial if life is to continue in
cold weather) Bipolar charge because of atom arrangement
-ve on oxygen side & +ve on hydrogen side bipolarity charge makes water stable and solvent for
many substances many chemical reactions can take place in water
Bipolarity makes water stable means large amount of energy needed to evaporate water large amount of energy has to be removed for
freezing water
Specific heat for water is among the highest amount of energy to raise 1 gram of substance by 1
C to heat 1 g water by 1 C requires 1 calorie or 4.186 J compare that to 1 g dry air (udara) which requires
1.006 J (about 1/4 less of that for water) this means water can absorb and release relatively
large amounts of heat with very little change in its temperature
high specific heat of water is one reason why oceans are much slower to respond to the heating or cooling of atmosphere
also why seasonal change in temperature of oceans are much less that that of the atmosphere
Hottest and coldest temperature ever recorded: on land: 58 C (Libya desert) and -88 C (Antarctica)
range = 146 C on ocean: 36 C (Persian Gulf) and -2 C (near poles)
range = 38 C only (much less than that for land) Ocean is a natural thermostat
annual sea surface temperature variation 2 C in tropics, 8 C in middle latitudes, 4 C in
polar regions global average ocean temperature 17 C releases and absorbs heat over decades to centuries,
whereas the atmosphere does the same but in days to weeks
Why is water still on Earth?Why is water still on Earth?
Earth’s atmosphere is layered troposphere (8-15 km) then stratosphere
Upper troposphere is very cold liquid water condenses into ice before it can reach
stratosphere, making the stratosphere very dry if water escapes into stratosphere and higher, UV
rays would dissociate water molecule into H and O H, being light, would not be held down by gravity and
would escape into space eventually all water would be lost from Earth this “cold trap” is essential to trap water on Earth
Hydrological cycleHydrological cycle
Capillary rise
Water entry into soil is called inflitration. Runoff is water flowing on the soil surface, unable to enter into soil (unable to inflitrate into soil)
(T)
(E)
Environmental soil physics by Daniel Hillel, 1998, Academic Press
Water balance within the root zoneWater balance within the root zone
Run in
RI + R + I + CR = + RO + ET + P
Balance looks deceptively simple, but some parameters are difficult to measure in practice, such as RI, RO, CR, P, and ET (especially the T component)
Water balance can be simplified by using some assumptions no irrigation, so I = 0 flat land or incoming water same as outgoing water by
runoff, so RI = RO deep water table (i.e., > 2 m), so CR = 0 balance over long term (i.e., a year), so no change is
soil moisture between the period, so = 0 Simplified equation:
R = ET + P this equation, though much simpler, has to be used
with care because it uses a lot of assumptions which may not be appropriate in some conditions
Carbon cycleCarbon cycle
Carbon cycle has a long term efffect on Earth’s climate Carbon cycle has two cycles
short-term cycle long-term cycle
Carbon exists mainly as gas CO2 in atmosphere
dissolved bicarbonate ions (HCO3-) in oceans
various organic compounds in soil Carbon is a major component in all living organisms
plants – 50% animals – 19%
Long term carbon cycleLong term carbon cycle
Carbonate rocks Organic carbon rocks
Surface carbon reservoirs:oceans (40)
atmosphere (0.75)biota (0.6)soil (1.6)
rockdegassing
rockdegassing
rock
wea
ther
ing
rock
wea
ther
ing
rock
bur
ial
rock
bur
ial
Rocks (75,000)
figures in trillion tonnes or teratonnes
Weathering (chemical breakdown) of rocks remove CO2 from the atmosphere CO2 reacts with water and silicate and carbonate
minerals to form, in water, Ca, Mg, bicarbonate ions, and silicia:
4CO2 + 6H2O + CaSiO3 + MgSiO3
Ca2+ + Mg2+ + 4HCO3- + 2H4SiO4
or
atmospheric CO2 + water + Ca and Mg silicate minerals
ions and species dissolved in river water
The dissolved ions wash into rivers which eventually flows into the sea. In the ocean, organisms use the dissolved Ca and bicarbonate ions to make shells:
Ca2+ + 2HCO3- CaCO3 + CO2 + H2O
or
Ca and bicarbonate ions in seawater
calcite + CO2 and water Dissolved silicate precipates to opal:
H4SiO4 SiO2.H2O + H2O
or
dissolved silica opal + water Mg is removed from seawater mainly by reacting with hot
rocks to form clay minerals
The carbonate shells accumulate at the ocean bottom and eventually form carbonate-bearing sedimentary rocks, such as coquina and chalk
With burial, these rocks heat up and compress, and the carbonate minerals break down to release CO2
the CO2 percolates out of the crust and escape into the atmosphere, completing the cycle
SiO2 + CaCO3 CaSiO3 + CO2
or
silicate minerals + carbonate minerals
calcium silicate minerals + carbon dioxide
Coquina, a limestone composed of fossilized shell debris cemented together by calcite
http://geology.about.com/od/more_sedrocks/ig/sedrocksgallery/coquina.--2t.htm
http://gccweb.gccaz.edu/earthsci/imagearchive/chemical1.htm
http://www.hunstantonfossils.co.uk/Hunstanton-Fossils-Geology/geology-guide.htm
Chalk, composed of fossilzed shells of microscopic organisms such as foraminifera
Role of photosynthesisRole of photosynthesis
Another route for CO2 to return to atmosphere:
removal of CO2 from the atmosphere by photosynthesis
then the burial of organic matter (OM) to make organic-rich rocks, primarily coal and carbonaceous shale
CO2 + H2O (CH2O)n + O2
where (CH2O)n represents carbohydrates, starches, and other organic compounds in plants
oxidation of sedimentary rocks as they are exposed by erosion or other physical breakdown returns CO2 into the atmosphere, completing the cycle
(CH2O)n + O2 CO2 + H2O
http://gccweb.gccaz.edu/earthsci/imagearchive/chemical1.htm
Coal Shale
http://www.geologytimes.com
Plate tectonicsPlate tectonics
CO2 can also be released from activities of Earth’s plate tectonics plate tectonics allow degassing of CO2 from rocks into
the atmosphere without plate tectonics, very difficult to return CO2 into
the atmosphere Earth would be frozen over
Plate tectonics is caused by the convection in Earth’s mantle this convection is, in turn, caused by the decay of
radioactive elements, mainly potassium (isotope 40K), thorium (Th), and uranium (U)
http://www.geography-site.co.uk/pages/physical/earth/tect.html
Plate tectonics akin to a jigsaw puzzle
http://www.crystalinks.com/platetectonics.html
MANTLE
http://facstaff.gpc.edu/~pgore/Earth&Space/GPS/platetect.html
Carbon regulation of climateCarbon regulation of climate
As CO2 increases, temperature increases due to greenhouse effect, so weathering of rocks increases. Why?
higher temperature may lead to higher rainfall (higher ET), so higher rate of weathering
higher CO2 or temperature may increase plant photosynthesis, so plants produce more organic acids and other compounds to increase rock weathering
As rate of rock weathering increases, more CO2 is removed from atmosphere, so this leads to cooling
But as Earth cools, the rate of rock weathering now slows down, and CO2 builds up in the atmosphere because of degassing by solid Earth
Almost all carbon on Earth is sequestered in rocks 6.5 x 1016 tons of C are in rocks but only 4.1 x 1013 tons of C are in other surface
reservoirs (1000 times less than in rocks) this balance is important: it keeps Earth from being
too cold (too much CO2 locked up in rocks) or too hot (too much CO2 released into atmosphere)
Short term carbon cycleShort term carbon cycle
Atmospherecarbon
Soilcarbon
Biotacarbon
Oceancarbon
Gas exchange
Rivertransport
Marine respiration
DegassingTerrestrialrespiration
Terrestrialphoto-synthesis
Marine photosynthesis
Litter fall, root decay,calcification
http://www.sheepdrove.com/312.htm
Short term carbon cycle refers to the circulation of carbon among the surface reservoirs (oceans, atmosphere, soil, and biota)
Photosynthesis removes carbon from atmosphere, and respiration returns it
Oceans absorb carbon from the atmosphere and releases it in smaller quantities colder the ocean, carbon can be absorbed easier warmer the ocean, harder to hold on to the carbon
analogy: cold Coke drink Soil adds carbon via degassing
decay of organic matter (higher the temperature, faster decaying rate)
Flow of carbon from one reservoir to another is well established but the amount and mechanisms of transport is not
well established yet Human activities, through burning of fossil fuels, add 6.3
Gt (gigatonnes or billion tonnes) carbon per year
http://www.globalchange.umich.edu/globalchange1/current/lectures/kling/carbon_cycle/Archive/carbon_cycle_2004.html
NET CHANGE = INPUT – OUTPUT
3.2 = (6.3 + 1.6) – (1.4 + 1.7)
3.2 = 4.8 ??!!
Carbon imbalance:
Where’s the rest of 1.6 Gt C?
The case of the “missing” carbonThe case of the “missing” carbon
Not all the amount of C added by human activities is found in the atmosphere
The ocean plays a critical role in determining amount of CO2 in the atmosphere on a long term time scale
Some of the anthropogenic C is stored in oceans and biosphere
Critical to know all the sinks if to accurately predict the expected climate change
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