Transcript The Sea Floor

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