Chapter 2 The Sea Floor

The Water Planet OCEANS Cover 71% of the globe Regulate earth’s climate and atmosphere

The Geography of the Ocean Basins Northern Hemisphere: 61% water Southern Hemisphere: 80% water

Ocean Basins Four Ocean Basins Pacific: Largest Atlantic Indian Artic: Smallest

The Structure of the Earth Earth = 4.5 Formed from the Big Bang:cosmic explosion of dust Occurred 13.7 billion years ago Dust Particles kept colliding until planets formed.

Early Earth Early earth was most-likely MOLTEN. As earth cooled: Densest material flowed toward center of earth. Lighter materials floated toward the surface.

Earth Began to Cool As Earth Cooled: Atmosphere formed Oceans formed

Internal Structure of Earth Core inner-most layer Composed of iron

Internal Structure of Earth Mantle Molten-solid rock Flows around core like liquid

Internal Structure of Earth Crust Outermost, best- known layer Thin Floats on Mantle

Two Types of Plates Make Up the Earth’s Crust ContinentalOceanic CompositionGraniteBasalt DensityLess DenseMore Dense Age (oldest rocks) 3.8 Billion Years Old200 Million Years Old Elevation Above Sea LevelBelow Sea Level

The Origin and Structure of Ocean Basins THE EARTH IS IN A STATE OF CONSTANT TRANSFORMATION.

Early Evidence of Continental Drift Sir Thomas Bacon (1620): noticed the coasts of continents fit together like puzzle pieces. Alfred Wegener (1912): Proposed continental drift hypothesis. “All Continents were once joined”: PANGAEA

Pangea

The Theory of Plate Tectonics Wegener’s hypothesis was not widely accepted because he could not explain HOW continental drift occurred.

The Theory of Plate Tectonics 1950s-1960s: Scientists had enough evidence to conclude that continents did “drift.” PLATE TECTONICS

Discovery of the Mid-Ocean Ridge Sonar lead to discovery during WW2 Continuous chain of volcanic mountains that encircle the globe

Significance of the Mid-Ocean Ridge The Sea floor is created at the Mid- Ocean Ridge

Magnetism of Ocean Floor Rocks BACKGROUND: Earth magnetic field reverses direction every few million years. Many rocks contain tiny magnetic particles & these move in molten rock. When the rock solidifies the particles freeze in their orientation Geologists found patterns of magnetic bands or stripes in the sea floor running parallel to the mid-ocean ridge The bands are symmetric around the ridge Magnetic bands = magnetic anomalies

How is the Sea-floor Created??? 1. Magma pushes through the mid- ocean ridge 2. Magma cools to form new sea floor 3. As more magma pushes through, the sea floor spreads out— SEA-FLOOR SPREADING

Sea-Floor Spreading & Plate Tectonics Earth’s surface is broken into plates. Plates are made of crust and top layer of mantle: LITHOSPHERE Plates spread 2-18 cm per year. (Fingernails grow 6 cm per year.)

Plate Movement As plates move, they collide with other plates. *USUALLY* Subduction Occurs: one plate is forced into the mantle when 2 plates collide.

Types of Collisions Oceanic- Oceanic Trenches (deep cracks in the crust) are formed.

Types of Collisions Continental- Oceanic Trenches produced.

Types of Collisions Continental- Continental: produces mountains.

Sliding Plates Sometimes plates slide past each other Faults are formed from this process Earthquakes are produced from this process

What Makes Plates Move??? SLAB PULL: oceanic crust becomes too heavy to float on the mantle and it sinks down into it, pulling the rest of the plate with it (slowly).

Geological History of the Earth Continents were once united: PANGAEA PANGAEA: began to break up 180 million years ago.

Geological Provinces of the Ocean

Types of Continental Margins Active: Narrow shelves Steep Slopes Little or no rise *Example: Pacific Coast of North America

Types of Continental Margins Passive Wide shelves Gentle slopes Well-developed rise *Example: Atlantic coast of North America

Deep Ocean Basins Deep-sea floor (ABYSSAL PLAIN): average of 4,000 m deep (13,000 ft)

Features of the Deep-Sea Floor Trenches :the deepest part of the ocean floor Rift Zone: break in the earth’s crust from which lava flows and new seafloor forms. Seamounts :submarine volcanoes Guyots: flat-topped volcanoes (INACTIVE) Abyssal Plain: flat part of seafloor Abyssal Hills : small hills Plateaus: flat-topped mountains

Guyots Flat-topped seamounts

Trenches Deepest parts of the ocean. Deepest: 36,163 ft.

Mid-Ocean Ridge and Hydrothermal Vents Central Rift Valley Located in center of Mid-Oceanic Ridge where plates are pulling apart.

Hydrothermal Vents Deep-sea hot springs Formed when water that has been heated by the mantle forces its way through the earth’s crust

Black Smokers Chimney-like structures Build up around vents Release “clouds” of minerals that have been heated by the vents