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What Lies Beneath
Pre Solar Nebula—4.6 Billion yrs ago
Protoplanetary Disk—50 million years later
Formation of the moon
Return of the Volatiles
Comets and Asteroids-lingering remnants of planetary formation
Oceans and Basalt
• Oceans cover 71% of Earth’s surface– 5 km deep on average, up to 11 km in trench
If the ocean floor is so deep, how do we study it?
Sampling Methods
• Collecting sediment/rock directly– Dredge
• Large net dragged along ocean floor
– Sediment Core• Weighty hollow pipe
dropped to ocean floor—sediment sample
– Drilling• Cylindrical cores of
sediment/rock
Remote Sensing
• Remote “sampling”– Magnetometers
• Instrument that measures a magnetic field
• Magnetic stripes
– Echo sounders• Sound signal from a
ship—deeper stuff=longer time to return to ship
Deep-sea Submersibles
Features of the Ocean Floor
Mid-Ocean Ridge System
Continuous, submarine mtn chain 80,000 km long rising an average of 2-3 km above the surrounding sea floor
Rift valley
Transform Faults
How Oceans Form
Life on the Seafloor?
Hydrothermal vents at a mid-ocean ridge.
• Black smokers– Hot water dissolves materials as it passes
through rock– Black color: fine- grained
metals that precipitate in “cool” ocean water
– 400°C sulfurous H2O
– Chemosynthesis• Bacteria feed on H2S
Ocean Trenches, Island Arcs
• Accreted Terranes
• Do the continents grow?
Seamounts and Guyots
• Basaltic seafloor features– Seamount: Submarine mountain, ≥1 km
above sea floor created by a hot spot– Guyot: a flat-topped seamount cut by waves
Wh Atoll Is It Made Of?
• Atoll: Circular coral reef forming a ring of islands around a lagoon– Lagoon: shallow, enclosed water basin
– Living coral keep up with rate of sinking
“Young” Oceans, Thin Sediments
• Why aren’t the seafloors as old as the continents?
• Structure of the ocean floor
Passive Continental Margins
• Contin. Shelf– Sedimentation
and Isostasy
• Contin. Slope– Thinner cont.
crust
• Contin. Rise– Apron of
debris
Carbonate Platforms
• In warm areas lacking In warm areas lacking terrigenous sedimentterrigenous sediment
– Thriving reef-Thriving reef- building organismsbuilding organisms
– Thick limestoneThick limestone beds accumulatebeds accumulate
Active Continental Margins
• Note thickness of shelf– Why is it only this size?