Earth’s Water: Origin of the Oceans Outline of the talk Spheres of the Earth System A few points...
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Transcript of Earth’s Water: Origin of the Oceans Outline of the talk Spheres of the Earth System A few points...
Earth’s Water: Origin of the OceansOutline of the talk
• Spheres of the Earth System• A few points from the Cosmosphere• A few points from the Geosphere• A few points from the Biosphere• Most likely Origin of Earth’s Water:
– Cooling of the primordial Earth– Water-rich asteroids but not comets– Leakage from hydrous minerals– Outgassing from cooling magma
• Use of Earth’s Water – the Anthroposphere • Future of the Hydrosphere
Spheres of the Earth System
H H
O
Earth System InteractionsThe Hydrological Cycle
Cosmosphere Geosphere Atmosphere Biosphere Hydropshere Anthroposp∙ ∙ ∙ ∙ ∙here
SpecificHeat
calories/gram/ºC
joules/kg/kelvin
Water 0.9998 4186
Air 0.2404 1006
Granite 0.192 804
Water is Unique
Molecular Structure
Heat CapacityOptical Properties
Surface Tension
And, ice floats!
• Asteroid – sometimes called minor planets or planetoids, are small solar system bodies in solar orbit
• Comet – a small object that orbits the sun whose nucleus is a loose collection of ice, dust, and small rocky particles
• Meteoroid – sand to boulder sized particle or debris in the solar system
• Planetary Habitable Zone – distance from sun where liquid water exists
Earth’s WaterA few points from the Cosmosphere
Earth’s WaterA few points from the Cosmosphere (con’d)
• Galactic Habitable Zone• Solar Habitable Zone
Galactic Habitable Zone Solar Habitable Zone vs. Star Mass (sun = 1)
Galaxy of Stars Our Variable Sun
Earth’s Water A few points from the Geosphere (con’d)
Earth’s Tectonic Plates
Motion of Tectonic Plates for the last 360 Million Years
The Origin of the Ocean A few points from the Geosphere (con’d)
• Oceans need:– Water– Basin
Black Smoker Cross-section of the North Atlantic Ocean
Earth’s Water A few points from the Biosphere
False-color enhanced biosphere variability today
Species on Earth Last 4 Billion Years
Origin of Earth’s WaterCooling of the primordial Earth
• Faint young sun paradox• Early greenhouse effect – carbonyl sulfide• O=C=S• OCS decomposes into CO and H2S in presence
of humidity: 2OCS+2H2O→2CO+2H2S+O2
• Snowball Earth ≈2.5 bya (2.5 billion years ago)
Earth before Water
The answer to the faint young sun paradox probably is Earth’s self-regulating system of returning CO2 to the atmosphere.
Carbonate-Silicate Cycle
Origin of Earth’s WaterBiosphere’s Role
Geosphere / Biosphere Interaction
Origin of Earth’s WaterHow much water from space?
• 10 million comets per year• Each comet weighs 10 kg• 4 billion years of accumulation• We need 1400 x 106 km3 (1400 million cubic km)
VCOMETS = 0.4 x 106 km3 NOT ENOUGH!
Origin of Earth’s WaterWater-rich asteroids but not comets
• Earth is believed to have formed hot and dry• Water in carbonaceous chondrites have a
similar deuterium to hydrogen (D/H) ratio as oceanic water
• D/H ratio of the three comets observed is approximately double that of oceanic water
• Asteroids or planetoids most likely source • Example: Saponite
Deuterium
Origin of Earth’s WaterLeakage from hydrous minerals
• Hydrous – a substance that contains water• Water escapes when heated• Earth’s mantle rock contains 0.1% to 0.5%
water by weight possibly from asteroids• Total mass of mantle rock is 4.5 x 1024 kg• We need 1400 x 106 km3 (1400 million cubic km)
VHYDROUS MINERALS = 4500 x 106 km3 TOO MUCH WATER!
Serpentine
Origin of Earth’s WaterOutgassing from cooling magma
• Hadean eon > 4.5-3.8 bya (from Greek Hades)– Concept in dispute– Early cool-Earth hypothesis
• Magma – fiery liquid silicate melt with volatile components such as fluorine, chlorine, water, carbon dioxide
• We need 1400 x 106 km3 (1400 million cubic km)
VOUTGASSING = 140000 x 106 km3 WAY TOO MUCH!
Volcano
Origin of Earth’s WaterCould we lose some of the excess?
• Formation of minerals• Example: Gypsum CaSO4·2H2O
• Role of Organisms: 4H2S+CO2→CH4+2H2O+4S• Photolysis: radiative breakdown of chemical
bonds in the atmosphere
A stratified atmosphere helps prevent loss of water and hydrogen
x1000 km3 % of total
Ocean 1,350,000.0 95.96
Cryosphere 43,400.0 2.97
Groundwater 15,300.0 1.05
All other reservoirs: 93.2* 0.02
Lakes* 9.0Rivers* 1.7Soil Moisture* 65.0Atmosphere* 15.5Biosphere* 2.0
Earth’s WaterWhere is Earth’s water now?
Earth’s Water
Volume (V) of Earth’s Water Today: V ≈ 1400 million cubic kilometers
Earth’s WaterEnd of Earth’s Water – the BIG picture
Boil Off
Eventually the sun will expand beyond Earth’s orbit, become a Red Giant star, then implode into a white dwarf star leaving behind a planetary nebula.
Seasons of Snow and Land Ice
Earth’s WaterQuestions?