Continental Margins• Continental shelf: shallowest part of the margin• Continental Slope: a steeper part• Continental Rise: gently sloping region at the

base of the of the continental slope; consists of sediment that piles up on the sea floor

Deep Sea Basins1. Abyssal plain: flat area

2. Seamounts: old volcanos and islands

3. Trenches: deepest part of the ocean

4. Mid Oceanic Ridge: main feature of the ocean floor

5. Central Rift Valley: great gap at the center where plates are pulling apart

Structure of Earth

• Earth Originated 4.5 billion years ago by the Big Bang

• Earth’s materials were sorted by density– Densest is found at

the center and the least on the outside

Structure of Earth

• Internal Structure– Inner Core: composed of Fe Ni,

high pressure and temperatures reach 5,000oC; solid in nature

– Outer Core: Same elements and temperature but less pressure so is a liquid

– Mantle: Contains Si and O, semi-solid state that moves like molasses

• Asthenoshere-upper mantle

– Crust: outermost layer, extremely thin, rigid skin floating on the mantle (Oceanic and Continental)

• Lithosphere-uppermost mantle and crust

Earth’s Crust• Continental Crust

– Consist of granite – 3.8 byo– Not dense and thick

•Oceanic Crust–Consist of Basalt–200 myo–Dense and thin

Continental Drift• Proposed in 1920 by

Alfred Wegener• Theory: states that all

the continents had once been joined in a single super continent called Pangaea, 180 mya

• Wegener was laughed at due his inability to proposed a mechanism for the movement of continents

Continental Drift

• Evidence– Coal deposits

– geological formations

– fossils match up on opposite sides of the Atlantic

– Jigsaw puzzle like appearance of continents

– Glacial rock deposits

– Limestone and salt deposits

Seafloor Spreading Evidence• Discovery of the Mid Ocean Ridge

– Discovered using sonar– Interrupted by large geological fault called

transform faults– EX: Mid-Atlantic Ridge and East Pacific Rise

Seafloor Spreading Evidence

• Magnetic Reversals– Discovered by the

Glomar Challenger in 1968

– Symmetric Pattern of Magnetic Bands in the seafloor from reversals of the magnetic poles

– Opposite matching bands on either side of mid-oceanic ridge

Seafloor Spreading Evidence

• Sediment Age and thickness

– Discovered by the Glomar Challenger

– Thickest and oldest sediments are found farthest from the Mid Ocean Ridge

Seafloor Spreading• Proposed by Henry

Hess in 1960’s• Theory: states that

mantle rises up at the Mid Ocean Ridges is then cooled, placed on the seafloor and moved towards the continents

• Mechanism was thought to be convection of the mantle beneath the seafloor

Plate Tectonics• Combination of

Continental Drift and Seafloor Spreading

• Theory: earth’s surface is covered by a fairly rigid layer composed of the crust and the uppermost part of the mantle called the lithosphere that is broken into plates which move over the mantle

Plate Collisions

• Oceanic Plate to Oceanic Plate– Causes trenches, earthquakes, volcanoes and island

arcs– EX: Aleutian Island in Alaska

Plate Collisions• Oceanic Plate and

Continental Plate– Creates a trench,

earthquakes, continental volcanoes

– Seafloor is destroyed at the trench which explains why the seafloor is so young

Plate Collisions

• Continental Plate and Continental Plate

– Create mountains– EX: Himalayan

Mountains

Plate Movements• Apart: plates do move

apart and create new crust– EX: mid ocean ridge

and Iceland

• Shear Boundary: plate are able to slide past each other– EX: California’s San

Andreas Fault

Marine Sediments

• Hydrogenous– Result from chemical reactions within seawater

• Cosmogenous– Result from outer space

• Lithogenous Sediment– Formed from the weathering and erosion of rocks

• Biogenous Sediment– Created from the skeleton or shells of marine organisms

– Calcareous: made of calcium carbonate

– Siliceous: made of silica

Hot Spots• Stationary plume

of magma under a moving plate

• Creates volcanic islands in the middle of plates

EX: Hawaiian Islands and the Emperor Seamount Chain