The Deep Oceans Take-Away Points 1. The earth has two kinds of crust 2. Continents have thick, light, granitic crust, Oceans have thin, dense, basaltic crust 3. How we probe the sea floor 4. Features on the sea floor and edges of continents are products of plate tectonics 5. Submarine landslides are important on continental margins 6. Deep ocean sediment comes from the continents and marine organisms The TwoStory Planet 1. The earth has two kinds of crust Earth Has Two Kinds of Crust 2. Continents have thick, light, granitic crust, Oceans have thin, dense, basaltic crust Continental and Oceanic Crust Continental Crust (Granitic) • Residue of Long-Continued Partial Melting • Thick and Light • Ancient: > 2.5 b.y. Oceanic Crust (Basaltic) • Derived Directly From Mantle • Thin and Dense • Young: < 200 m.y. 2. Continents have thick, light, granitic crust, Oceans have thin, dense, basaltic crust Investigating the Sea Floor • • • • • • Coring Deep-Sea Drilling Sonar Seismic Refraction Gravity Surveys Magnetic Surveys 3. How we probe the sea floor Piston Coring 3. How we probe the sea floor Deep Ocean Drilling Project Mohole • Original Intent: Drill to Earth’s Mantle • Drill in Oceans where Crust is Thinnest • Hidden Agenda: Complete History of Oceans • Challenge: Replacing Drill Bits in 5 km of Water • Plate Tectonics Showed that Mantle is Exposed in a Number of Places 3. How we probe the sea floor Deep Ocean Drilling • Original Objective Abandoned • Renamed Deep Sea Drilling Program • Now Called Ocean Drilling Program 3. How we probe the sea floor Sonar 3. How we probe the sea floor Seismic Refraction 3. How we probe the sea floor Makeup of Ocean Crust 4. Features on the sea floor and edges of continents are products of plate tectonics Anatomy of a Mid-Ocean Ridge Continental Margins • • • • Shelf Slope Rise Active: Subduction Zones. Sometimes Called Leading Edge • Passive: No Subduction. Sometimes Called Rifted or Trailing Edge 4. Features on the sea floor and edges of continents are products of plate tectonics A Continental Margin 4. Features on the sea floor and edges of continents are products of plate tectonics Evolution of a Passive Margin 4. Features on the sea floor and edges of continents are products of plate tectonics Anatomy of a Passive Margin 4. Features on the sea floor and edges of continents are products of plate tectonics Features of the Deep Ocean • Mid-Ocean Ridges • Abyssal Plains • Fracture Zones • Oceanic Trenches • Seamounts • Submarine Canyons • Submarine Fans 4. Features on the sea floor and edges of continents are products of plate tectonics Crest of the MidAtlantic Ridge 4. Features on the sea floor and edges of continents are products of plate tectonics Sea-Floor Spreading, Mid-Atlantic Ridge 1. Features on the sea floor and edges of continents are products of plate tectonics Turbidity Flows – Grand Banks, 1929 5. Submarine landslides are important on continental margins Where Sediment Comes From 6. Deep ocean sediment comes from the continents and marine organisms Atlantic Sediments Deep Ocean Sediments 6. Deep ocean sediment comes from the continents and marine organisms Take-Away Points 1. The earth has two kinds of crust 2. Continents have thick, light, granitic crust, Oceans have thin, dense, basaltic crust 3. How we probe the sea floor 4. Features on the sea floor and edges of continents are products of plate tectonics 5. Submarine landslides are important on continental margins 6. Deep ocean sediment comes from the continents and marine organisms