Earth’s Water: Origin of the Oceans Outline 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 HH O

Earth System Interactions The Hydrological Cycle Cosmosphere∙Geosphere∙Atmosphere∙Biosphere∙Hydropshere∙Anthroposphere

Specific Heat calories/ gram/ºC joules/ kg/kelvin Water Air Granite Water is Unique Molecular Structure Heat Capacity Optical 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 Water A few points from the Cosmosphere

Earth’s Water A 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 StarsOur 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 Water Cooling of the primordial Earth Faint young sun paradox Early greenhouse effect – carbonyl sulfide O=C=S OCS decomposes into CO and H 2 S in presence of humidity: 2OCS+2H 2 O→2CO+2H 2 S+O 2 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 CO 2 to the atmosphere. Carbonate-Silicate Cycle Origin of Earth’s Water Biosphere’s Role Geosphere / Biosphere Interaction

Origin of Earth’s Water How much water from space? 10 million comets per year Each comet weighs 10 kg 4 billion years of accumulation We need 1400 x 10 6 km 3 ( 1400 million cubic km ) V COMETS = 0.4 x 10 6 km 3 NOT ENOUGH!

Origin of Earth’s Water 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 Deuterium

Origin of Earth’s Water Leakage 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 kg We need 1400 x 10 6 km 3 ( 1400 million cubic km ) V HYDROUS MINERALS = 4500 x 10 6 km 3 TOO MUCH WATER! Serpentine

Origin of Earth’s Water Outgassing from cooling magma Hadean eon > 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 10 6 km 3 ( 1400 million cubic km ) V OUTGASSING = x 10 6 km 3 WAY TOO MUCH! Volcano

Origin of Earth’s Water Could we lose some of the excess? Formation of minerals Example: Gypsum CaSO 4 ·2H 2 O Role of Organisms: 4H 2 S+CO 2 →CH 4 +2H 2 O+4S Photolysis: radiative breakdown of chemical bonds in the atmosphere A stratified atmosphere helps prevent loss of water and hydrogen

Earth’s Water Where is Earth’s water now? Earth’s Water Volume (V) of Earth’s Water Today: V ≈ 1400 million cubic kilometers

Earth’s Water End 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 Water Questions?