Transcript The Seafloor

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 23 km above the surrounding sea floor
Rift valley
Transform Faults
How Oceans Form
Life on the Seafloor?
• Black smokers
– Hot water dissolves materials as it passes
through rock
– Black color: finegrained metals
that precipitate in
“cool” ocean water
– 400°C sulfurous H2O
– Chemosynthesis
• Bacteria feed on H2S
Hydrothermal vents at a mid-ocean ridge.
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
terrigenous sediment
– Thriving reefbuilding organisms
– Thick limestone
beds accumulate
Active Continental
Margins
• Note thickness of shelf
– Why is it only this size?