Transcript Commotion Beneath the Ocean

Commotion Beneath the
Ocean
Introduction to Plate Tectonics
Plate Tectonics
• Originally proposed by Wegener - but
ridiculed !!
• 1960’s new evidence found
• Earth’s Surface Continually Shifting
• Plate - Large, Rigid Slab of Solid Rock
• Tectonics- to build
Theory of Continental Drift
• Pangaea
– 225 mya
• Earth/Solar System
- 4.6 bya
• Life
– 3.4 bya
Evidence of Continental Drift
• Coastline shapes
• Rocks Minerals
• Fossils
Inside the Earth
• Crust
• Mantle
• Core
Convection
• Heated material
expands - becomes
less dense - more
buoyant
• It rises and cold
material takes it’s
place
Heat
• Decay of
Radioactive
Elements inside
Earth
• Trying to Escape
• Convection transport of mass by
heat (heat changes
the density)
Mid- Ocean Ridges
• Sonar
• Mapping Began
during WWII
• By 1960’s clear
maps of mid ocean
ridges
Ocean Maps
• All the major oceans
have long ridges
Underwater Volcanoes
• Opening of the earth
where hot molten
rock, ash, and
gases to escape
from deep below the
surface
• Underwater
volcanoes are called
Hydrothermal vents
So what do the ridges have to
do with plate movement?
• Undersea volcanoes
• Deposit molten rock
from mantle
convection
• Seafloor spreading Supported Theory of
Plate Tectonics 1962
- Harry Hess
Seafloor Spreading
as proposed by Harry Hess
• New Ocean Floor
deposited at the ridges
• Moves laterally away
from the ridges
• Moves back down at
the continental margin
• Continents are not
“islands” they are parts
of larger plates that
move on the soft
asthenosphere
Earth’s Magnetic Field
• Liquid Iron in the outer
core
• Moving Electrical
charges (current)
INDUCE a magnetic
field
• Aligns approximately
with the spin axis but
periodically flips
N<-->S
Evidence for Seafloor Spreading
• Magnetic Reversals
• Rocks have magnetic
fields
• When rocks cool
magnetic minerals align
to Earth’s Mag Field
• 1960’s drilling found
Mirror images on each
side of mid Atlantic
ridge
How old is the lithosphere?
• Dates of rock
increased on
both sides of
mid-ocean ridges
The Plates
• Earth - egg
• Shell - cracked,
but stronger than
the interior
• Tectonic plates in the lithosphere
Plates
• Tectonic plates are in
the lithosphere
• The lithosphere floats
on the Asthenosphere
• Asthenosphere is
undergoing convection
• Plates are moving and
interact with other
plates
Plate Boundaries
Transform
Divergent
Convergent
Divergent Plates
• Lithosphere is being
produced
• Happens at mid
ocean ridges
• Plate motion is away
from the boundary
• Sea-floor spreading
• Well if two plates are
diverging…..
Convergent Boundaries
• Lithosphere sinks
back into the
asthenosphere (its
recycled)
• One plate moves
under another plate
- SUBDUCTION
• The ocean plate is
denser !!
Continent - Continent
When two continental
crusts converge, the
result is a huge mountain
range.
Both pieces of crust are
buoyant.
Example - Himalayas
Indian plate -->> Asian
plate.
Numerous earthquakes
but very little volcanism.
Transform Plate Boundaries
• One plate slides
parallel to
another plate
• San Andreas
Fault
•
• Plate
boundary
details for
the West
Coast of
North
America
Divergent Plate Boundaries
Hot Spots and Hawaiian
Islands
• 1963 Tuzo Wilson (also
discovered transform
faults)
• Noticed Volcanism in
some areas active for a
really long time
• Heat produced magma,
melted through the
plates.
• Magma lighter than the
rock rises.
Hawaiian Chain
Hot Spots
Measuring Hot Spots
• Yellowstone
• Plate moves
• Hotspot does not
• Determine and compare
the age of the rocks
•
New evidence shows that hot
spot may also move somewhat
Hot Spots
• Yellowstone:
several craters
or calderas
Energy fuels hot
springs and
geysers - Old
Faithful
May be a Super
Volcano !!
Review