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?