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Geosphere III The Origin of the Ocean

Geosphere III The Origin of the Ocean. Dr. George A. Maul OEC Room 258 gmaul@fit.edu. A Brief History of Water. The Origin of the Ocean Outline of the class. A few points from the Cosmosphere A few points from Geosphere I and II Most likely contributing factors:

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Geosphere III The Origin of the Ocean

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  1. Geosphere IIIThe Origin of the Ocean Dr. George A. Maul OEC Room 258 gmaul@fit.edu A Brief History of Water

  2. The Origin of the OceanOutline of the class • A few points from the Cosmosphere • A few points from Geosphere I and II • Most likely contributing factors: • Cooling of the primordial Earth • Water-rich asteroids but not comets • Leakage from hydrous minerals • Outgassing from cooling magma • Future volume of Earth’s Hydrosphere

  3. But first a bit of humor

  4. The Origin of the Ocean A few points from the Cosmosphere • 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 the sun where liquid water exists

  5. The Origin of the Ocean A few points from the Cosmosphere (con’d) • Galactic Habitable Zone • Solar Habitable Zone

  6. The Origin of the Ocean A few points from the Geosphere • Isostasy – floatational property of the lithosphere on the viscous asthenosphere • Asthenosphere – balance between temperature and pressure (p) such that rock is very close to melting • Lithosphere – continental crust is less dense (ρ) than oceanic crust Hydrostatic Equation p = ρgh

  7. The Origin of the Ocean What is the pressure below the lithosphere? • pressurelithosphere = 2.7 g/cm3x 980.6 x 25 km x 105 cm/km • pressurelithosphere = 2700 kg/m3x 9.8 x 25000 m • pressurelithosphere = 6.6 x 108 pascals • About the same as below the ocean’s crust • About 6500 atmospheres • All of the above Why?

  8. The Origin of the Ocean A few points from the Geosphere (con’d) • Oceans need: • Water • Basin • Salt Scale = distance on chart ÷ distance on Earth Vertical Exaggeration = Horizontal Scale ÷ Vertical Scale

  9. The Origin of the Ocean A few points from the Geosphere (con’d) • Continental Margins • Passive continental margins • Continental convergent margins • Continental collision margins • Transform fault margins • Accreted terrane margins • Seafloor spreading

  10. The Origin of the Ocean A few points from the Geosphere (con’d) • Continental Margins • Seafloor spreading Robert S. Dietz

  11. The Origin of the Ocean How much water in today’s ocean? • Volume (V) = Area (A) · Depth (Z) • ASPHERE = 4πr2 • rEARTH = 6378 km • AOCEAN = 71% of Earth • ZOCEAN = 3.72 km • VOCEAN = ? (units?) All Earth’s water (left); air (right) at sealevel VOCEAN = 1,350 x 106 km3

  12. The Origin of the Ocean Cooling 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

  13. The Origin of the Ocean Carbonate-Silicate Cycle The answer to the faint young sun paradox probably is Earth’s self-regulating system of returning CO2 to the atmosphere. CO2+H2O H2CO3 How many spheres are involved? CaSiO3

  14. The Origin of the Ocean Water-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

  15. The Origin of the Ocean How much water from space? • 10 million comets per year • Each comet weighs 10 kg • 4 billion years of accumulation • Mass (M) of water? • M = 10x106 comets/year x 10 kg/comet x 4x109 years = 4x1017 kg but ρWATER = 103 kg/m3 • 4x1017 kg ÷ [(103 kg/m3)x (103m/km)3] = VCOMETS = 0.4 x 106km3 NOT ENOUGH!

  16. The Origin of the Ocean Why did the drop bounce? • thermal expansion • surface tension • electrical conductivity • refraction • specific heat • salinity • density

  17. The Origin of the Ocean Leakage from hydrous minerals • Hydrous – a substance that contains water • Water escapes when heated • Example: Gypsum CaSO4·2H2O • Example: Serpentine (Mg,Fe)3Si2O5(OH)4 • Role of Organisms: 4H2S+CO2→CH4+2H2O+4S • Photolysis: radiative breakdown of chemical bonds on the surface • Respiration: C6H12O6+6H20+6O2→6CO2+12H2O

  18. The Origin of the Ocean Leakage from hydrous minerals? • Earth’s mantle rock contains 0.1% to 0.5% water by weight • Total mass of mantle rock is 4.5 x 1027 grams • 4.5 x 1027 g ÷ 103 g/kg = 4.5 x 1024 kg 4.5 x 1024 kg ÷ ρWATER = 4.5 x 1021 m3 4.5 x 1021 m3 x 0.1% = 4.5 x 1018 m3 4.5 x 1018 m3 ÷ 109 m3/km3 = VHYDROUS MINERALS = 4500 x 106 km3 TOO MUCH WATER!

  19. The Origin of the Ocean Outgassing 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 • Water recycled?

  20. The Origin of the Ocean How much water from outgassing? • 3.5 x 101 km3 per year • 3.5 x 101 km3/year x 4 x 109 years = VOUTGASSING = 140000 x 106km3 TOO MUCH!

  21. The Origin of the OceanFuture volume of Earth’s Seas • Assuming minimal loss to space and a steady-state recycling through plate tectonics • Input from space • Glacial melt • Sea Level Rise If all the land ice melted, how much would global sea level rise? Height=Volume ice ÷ AreaEarth =43.4x106km3 ÷ 4π(6378km)2 Height ≥ 85 meters

  22. Sea Level Over Time Last 140,000 years Maximum rate = 1 cm/year Last 18,000 years

  23. Relative Sea Level • Earth’s sea-level changes on time-scales of the twice-daily tides to millennia. • Relative sea-level (RSL) is the relationship between the water and the land. • If the land is sinking, relative sea-level is rising, and if the land is rising, sea-level appears to be falling. Tide gauge

  24. Factors AffectingRelative Sea Level (RSL) Change RSL = Height thermal expansion + Height land motion + Height glacial melt + Height ocean circulation + Height winds + Height barometric pressure + Height tides + Residual

  25. Future Sea Level? Projected sea level to 2100 The current rate of Florida relative sea level rise = 2.3 mm/year. How long will it take for relative sea level to rise 1 meter (3.28 feet)? Factors affecting future climate and sea level 1000 mm ÷ 2.3 mm/year = 435 years

  26. QUESTIONS?

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