Transcript oceans

• Study of the development and physical
characteristics of our planet’s seafloor
and continents and the forces that shape
• How did the oceans and continents form?
Big Bang
• 20 billion years ago
• Matter (all elements in periodic table)
expanded into space
• Matter clumped and planets formed 5 bya
• Early on our planet is a hard rock being
bombarded by other planetary bodies
and experiencing volcanic eruptions
82 percent of meteorite falls are chondrites
Formation of Earth’s Layers
1. Heating (leftover radioactive heating)
Denser (Fe and Ni) material sunk to the center
Lighter (Si and O) material rose to surface
Some materials vaporized to form early oceans
and atmosphere
2. Layers formed
3. Planet cools
Our “usual” image of Earth
Evidence for layers from Seismic
Early Atmosphere
• 3.5 bya
• Water vapor, carbon monoxide, hydrogen
sulfide, nitrogen and cyanide
Early Oceans
• 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 the Continents
• Alfred Wegener suggested the continents
were not always on their present positions
• Continental Drift
• 200mya 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
• Wegener was a meteorologist…what did
he know anyway!!!
– 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 1 cm/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 like the Mid-Atlantic Ridge
Moving Plates
• Sea floor spreading- plates move apart
from rising magma at a ridge
• Subduction- two plates collide and the
denser plate sinks into the mantle
– Forms trenches (Marianas Trench)
– Trenches are the deepest parts of the
Ocean Floor Formation
• Sea floor spreading is source of new
ocean floor
• Subduction recycles ocean floor back into
the mantle
• Atlantic is growing
• Pacific is shrinking
Sea Floor Spreading Evidence
• Younger rocks are found closer to the
• Less sediment closer to the ridge
• Polarity of magnetic minerals is mirror
image on either side of the ridge
– N and S pole flip periodically
– Minerals line up as magma cools with
the N pole
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
Why We Have Oceans & Why The
Ocean Floor Is Not Flat
Ocean Floor Topography
• Average ocean depth is 3636 m
• Sonar is used to map features of
the ocean floor
• The study of elevations and
depressions is topography
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.
2 Types of Crust
•Continental crust
•less dense (lighter)
•floats on the mantle
•35- 70 km thick
•3500 million years old
•Oceanic Crust
•6 Km thick
•Younger than 200 million years
•Sinks into mantle
Typical Features
• Continental Shelf-extension of the
• Continental Slope- steep drop off from
shelf and end of the continent and it’s
• 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
Plate Tectonics and Continental Coastlines
• Active margins (California)
–Sites of tectonic activity earthquakes, volcanoes,
–Narrow c. shelf and steep
slope ending in trench
• Passive
–Little to no tectonic activity
–Wide shelf, pile of sediment at
the bottom of the slope
Plate Margins
• Converging plates
–O & C- oceanic subducts under
continental: trenches, volcanic
islands & earthquakes
–O & O- one plate subducts
under the other: trenches,
volcanic islands & earthquakes
–C & C- mountains&
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
• Chemosynthesis- make sugars
using energy from compounds
like H2S
• Other vent animals include giant
tubeworms, crabs, octopus,
shrimp and mussels
• Nature of our planet and its changes
• Impact on human life
• Predicting future natural disasters
Distribution of our Oceans
• Cover ¾ of our planet
• Southern hemisphere is 80% ocean while
Northern hemisphere is 60% ocean
• Separate but connected basins
• Include features like…
• Most of the ocean bottom is an abyssal
Ocean Bottom Review
Ocean basin
• Continental shelf
• Narrow shelf
• Wide shelf
Continental Margins
– Trench
– Abyssal plain
• Outer layer of our planet move and deform
• Boundary
• Converging
• Diverging
• Transform
• Continental drift
• Sea floor spreading
– Diverge
– Ridges
• Subduction
– Converge
– Trenches