Requirements for ocean formation
Sea Water Evolution
Lauren Toth
• Lots of liquid
• Large amounts of ocean elements- H, O,
C, N
• Liquid must occur at STP- why we have
oceans of water not methane or ammonia
• Basin- tectonics
• Sufficient gravity
Photo by: Phil MacDonald
Early Ocean History
• Released from crust and upper mantle
during the early Archean
• Alternate theory: Icicles from space
• Recycling of oceans
• Na and Cl were the major ions
– Also K, Mg, Ca
From Degens 1989
Soda Ocean Concept
• Henderson-Sellers
and Cogley
• Low pCO2 in
atmosphere
• High (>9) pH
• Precipitation of
sodium carbonate
Na2CO3
From Degens 1989
Transition to Halite Ocean
• Removal of carbonates over time
– Movement into sediment pore water
– Incorporation into crust
– Subduction
– Biological use and burial
From Degens 1989
Aragonite and Calcite
• Both forms of calcium carbonate CaCO3
• Calcite is more stable
• Currently, our seas a aragonitic
• Leaching on Cl from crust and weathering
• Acids like HCl
From Degens 1989
www.beg.utexas.edu/.../graphics/calcite.htm
www.jewelsforme.com/Aragonite.asp?gemtype=GS
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Aragonitic vs. Calcitic Seas
• Shifts have 100-200My periodicity
• Aragonite dominates when Mg/Ca ratio is
high
– Evaporates of MgSO4
• Calcite dominates when Mg/Ca is low
– Evaporates of KCl
• Shifts in pH may also contribute to
switches
Hardie 1996
The role of seafloor spreading
• Hydrothermal brine
• Small changes in midocean ridge
spreading rates can
mean large changes
in ocean chemistry
• Spreading depletes
Mg and SO4 and
produces huge
increases in Ca
Hardie 1996
Mg/Ca
• <2 produces low Mg
calcite
• 2-5.3 produces high
Mg calcite and
aragonite
• 5.3 produces
aragonite
Hardie 1996
Hardie 1996
Hardie 1996
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Evolution of calcification
• Rise in Ca leading up to the Cambrian
explosion
– Looked at fluid inclusions using SEM to
determine Ca content
– Depleted in Mg and SO4
• Why?
– Defense
– Detoxification
Calcification today
• Corals, green algae,
some mollusks, and
some red algae use
aragonite
• Echinoderms and
most red algae use
high-Mg calcite
• Formaniferans use
low-Mg calcite
http://scienceblogs.com/voltagegate/2007/05/global_warming_conclusively_li.php
http://sealevel2.jpl.nasa.gov/jr_oceanographer/images/o-sager-cocolit1.jpg
www.reefcorner.com/SpecimenSheets/halimeda.htm
commons.wikimedia.org/wiki/Image:Seaurchin.jpg
Brennan et. al 2004
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