The Sea Floor

A: Right! The Southern Hemisphere contains nearly 80% water by volume. Brain Warmers: Q: Of the Norhern and Southern Hemisphere, which one contains the most water?? A: Right! The Southern Hemisphere contains nearly 80% water by volume. Q: Which ocean is the largest? The deepest? a. Arctic b. Pacific c. Atlantic d. Indian A: Pacific A: Pacific again!

Figure 2.02

How did it all get this way? Big bang leftovers! Density played a major role. How’s that work?? Density = mass/volume Lighter stuff stays on the top!

Figure 2.03

Ocean Floor Facts Ocean crust is composed of basalt. Basalt is common to the sea floor also. Much of the crust which forms land masses is composed of granite. Much of the ocean floor and crust differs in age too! (200 myo compared to 3.8 byo!!) Why??

Ocean Floor Structure Sir Francis Bacon (1620) considered contents puzzle pieces. Geological features (coal deposits) matched on opposite coasts.

Ocean Floor Structure Sir Francis Bacon (1620) considered contents puzzle pieces. Geological features (coal deposits) matched on opposite coasts. Alfred Wegner (1912) hypothesized continental drift.

180 mya Pangea Bound… Continents may have been one piece which later broke apart, moved, and formed present day conditions. How?? Plate tectonics ocean floor movement. Consists of faults (cracks) which form the mid ocean ridges (mountains). 150 mya 95 mya 45 mya 15 mya

Current Mid-ocean ridges & trenches Figure 2.05 Current Mid-ocean ridges & trenches

These locations are a significant source of geological activity! Figure 2.06 These locations are a significant source of geological activity!

Figure 2.07

Magnetic anomalies occur here too! Figure 2.08 Sea floor spreading occurs at mid-ocean ridges. Magnetic anomalies occur here too!

Sea-floor spreading where the ocean floor moves away from the mid-ocean ridge records the magnetic fields of the earth.

Locations and direction of seafloor spreading. Figure 2.10 Locations and direction of seafloor spreading.

Crust and mantle come together to form the lithosphere. Figure 2.11 Crust and mantle come together to form the lithosphere. Subduction and resulting subduction zones where ocean floor plates flow beneath the mantle of the crust are places of tectonic activity.

Trenches and island arcs can be formed when two sections of ocean Figure 2.12 Trenches and island arcs can be formed when two sections of ocean plates come together.

Some areas can be quite acitve!! Figure 2.13 Mt. Veniaminof, Alaska Some areas can be quite acitve!!

Shear (transform) boundary. Figure 2.14 When plates move sideways then a new formation called a Shear (transform) boundary. San Andreas Fault, CA

Figure 2.15 Swirlling vs. Pulling Convection suggests that continents move on a “soup” of rock, Whereas slab pulling indicates that as rock cools, it sink beneath the surface and “pulls” lithosphere into the depths (This is the currently accepted explanation.)

CONTINENTAL MARGIN (boundary between oceanic crust & continental crust) Continental Shelf – shallow, flat, most life Shelf Break - shelf abruptly deepens Continental Slope - edge of continent Continental Rise - sediment build up at slope base

Figure 2.20

Figure 2.21

Figure 2.22

ABYSSAL PLAIN (DEEP SEA FLOOR) 10,000 – 16, 500 ft deep

Generally flat except for: Seamounts – submarine volcanoes

Text Art 2.02

Guyots – flat-topped seamounts (inactive)

Heated water emerges through rift cracks Water 68F – 660F HYDROTHERMAL VENTS (DEEP SEA HOT SPRINGS) Found in mid-ocean ridge depression called “Central Rift Valley” Heated water emerges through rift cracks Water 68F – 660F Water dissolves toxic minerals (sulfides) which solidify

Black Smoker

The first organisms to populate the vents are bacteria, then other microorganisms, including amphipods and copepods appear. These are followed by limpets (snails), shrimp, crabs, tube worms, fish, and octopi. Sometime later acorn worms, dandelion-like animals, and other species of shrimp and tube worms add to the expanding community. In their most advanced stages vents are home to mussels, a variety of worms, anemones, and a large population of crabs, as well as many of the earlier colonists.