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?