Geosphere III The Origin of the Ocean

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

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. 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 water exists

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

5. 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

6. 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?

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

8. 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

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

10. 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 = 3.8 km • VOCEAN = ? (units?) All Earth’s water (left); air (right) at sealevel VOCEAN = 1,397 x 106 km3

11. 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

12. 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?

13. 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

14. 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 = 4 x 105 km3 NOT ENOUGH!

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

16. 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+6O2→6CO2+6H2O

17. 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 = 4.5 x 109 km3 TOO MUCH WATER!

18. 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?

19. 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 = 1.4 x 1011 km3 TOO MUCH!

20. 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

21. 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

22. Sea Level Over Time Last 140,000 years Last 18,000 years

23. 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

24. QUESTIONS?