The Sea Floor

Distribution of the Worlds Ocean 71% of the earth is covered by water. Four large basins Pacific, Atlantic, Indian, Arctic. Southern hemisphere is 80% ocean while Northern hemisphere is only 60% ocean. Separate by connected basins Include features like…. Most of the ocean bottom is an abyssal plain

Have you ever wonder why our planet has oceans? The theory of plate tectonics can explain the presence and features of the ocean basins on our planet…

The Sea Floor Geology: Study of the development and physical characteristics of the planets sea floor and continents and the forces that shape them. How did oceans and continents form?

Big Bang Theory 15 Billion years ago Matter expanded into space. Earth and Solar system originated from a cloud or clouds of dust. Dust particles collided with each other – those larger particles collided with one another – then those larger particles collided with one another, and so on…

Formation Of Layers Heating Denser (Fe and Ni) material sunk to the center. Lighter (Si and O) material rose to the surface. Some materials vaporized to form early oceans and atmosphere. Layers Form Planet Cools

Image of Earth

Early Atmosphere Water vapor, carbon monoxide, hydrogen sulfide, nitrogen and cyanide

4 bya water vapor from mantle is cooled and collects on surface. 1000’s of years of thunderstorms and rain Low lying spots fill to become our early oceans Water also from comets, volcanoes, meteors, geysers, rocks that contain moisture

Origin Of Continents Alfred Wegher suggested the continents were not always on their present positions. Continental Drift 200 mya, A single landmass called Pangea broke up.

Evidence… Coastlines fit like a puzzle. Similar fossils and rock formations on different continents.

Problems with CD No mechanism for how the continents “drift” Wegener was a meteorologist…what did he know anyway!!!

CRUST –thin outer layer less dense, rocks that floated to the surface when the Earth was formed between 35km and 70km thick. –not a continuous layer of rock Split into plates, which are free to drift slowly across the surface of the planet.

Moving Plates Continents move 1cm/yr Boundary between plates is a FAULT Seismic activity occurs at faults The lower mantle is heated by the core which creates convection currents. Rising magma may break thru the crust at ridges…. i.e. mid-atlantic ridge.

Moving Plates Spreading sea floor –plates move apart from rising magma ridge Subduction – Two plates collide and the denser plate sinks into the mantle Forms trenches.

Ocean Floor Formation Sea floor spreading is the source for new ocean floor. Subduction recycles ocean floor back into the mantle

Subduction and Trenches

Sea Floor Evidence Young rocks are found closer to the ridge. Less sediment closer to the ridge Magnetic bands Minerals line up as magma cools with N pole. N and S pole flip periodically.

Plate Tectonics Unifying theory that combines continental drift and sea floor spreading. Explains the origin of connections between earthquakes, volcanoes, faults, continental drift, and sea floor spreading. Explains how oceans and its features are formed.

Why the ocean floor is not flat?

Oceanic crust is denser than continental crust sinks lower into the mantle This is why it is filled w/ water and has become an ocean basin.

Typical Features Continental Shelf-extension of the continent Continental Slope- steep drop off from shelf and end of the continent and it’s crust Submarine Canyons- deep valleys in the slope created by underwater landslides or old rivers Continental Rise- a pile of sediment that has slid down the slope Seamounts and Guyots- Islands created by underwater volcanoes

Features of Ocean Ridges Water is superheated (371 C) by hot magma and dissolves minerals from nearby rock As water comes out from the rock it looks like smoke Area with these hot springs is called a hydrothermal vent

Animals from hydrothermal vents Bacteria are the base of the food chain Chemosynthesis- make sugars using energy from compounds like H2S Other vent animals include giant tubeworms, crabs, octopus, shrimp and mussels