The Deep Oceans

Take-Away Points1. The earth has two kinds of crust2. Continents have thick, light, granitic crust,

Oceans have thin, dense, basaltic crust3. How we probe the sea floor4. Features on the sea floor and edges of

continents are products of plate tectonics5. Submarine landslides are important on

continental margins6. Deep ocean sediment comes from the

continents and marine organisms

The Two-Story 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 CrustContinental 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 DrillingProject 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 Mid-Atlantic 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 Points1. The earth has two kinds of crust2. Continents have thick, light, granitic crust,

Oceans have thin, dense, basaltic crust3. How we probe the sea floor4. Features on the sea floor and edges of

continents are products of plate tectonics5. Submarine landslides are important on

continental margins6. Deep ocean sediment comes from the

continents and marine organisms