Plate Tectonics

Plate Tectonics
Earth’s Layers
The crust
• Lithosphere- rigid, top of the mantle and
Convetion Currents in the Earth's Crust
• Asthenosphere- softer and hotter layer
• They move like pavement resting on hot tar
The lithosphere looks like a jigsaw
puzzle…on the surface of the earth
• Tectonic plates- large slabs of rock parts of
ocean crust and continents rest on.
• Geologists study earth processes such as
landslides, earthquakes, floods and volcanic
• Geologists work to understand the history of
our planet. The better they can understand
Earth’s history the better they can foresee
how events and processes of the past might
influence the future.
Alfred Wegener
• A geologist who first proposed
continental drift theory in 1912
• His hypothesis was that all of earth’s
continents were once one giant land
• Gradually they drifted apart
• His scientist peers and friends did
not agree until the middle of the
Evidence for Continental Drift
• 1. Fossil Record: the fossil of the same ancient
reptile was found in both South America and
southern Africa, but no other place in the world.
Both continents must have been joined together at
some time in the past.
Evidence for Continental Drift
• Evidence of Climate change• Fossils of ancient ferns from
jungles exist on Greenland,
which is now covered in ice.
Greenland must have once
been near the equator.
• Evidence of glaciers existed in
South Africa, where the
climate is now a jungle and
desert in parts.
Evidence for Continental Drift
• Geology- rock typing found on different
continents matches up. Rocks from Brazil
matches up with Africa.
Carbonado diamondites
supernova rocks that
impacted on Earth in the
Brazil and Central African
Republic area (these were
originally next to each
other, before the ancient
Gondwana continent rifted
Rock Evidence
• Pangaea was formed 270 mya during the
Permian and Triassic time periods of Earth’s
• Most of the dry land was joined together into
one huge land mass.
• The Permian mass extinction, which wiped out
an estimated 96% species about 248 million
years ago, was a major event during this time.
• Pangaea began to split apart 200 mya
New Technology, New Discoveries
• Scientists began mapping the sea floor
• Using drilling, SONAR, lasers bounced off of
satellites, and undersea explorers, they
started making detailed maps of the sea bed.
• These discoveries gave evidence of
continental drift and how the tectonic plates
Sea Floor Spreading
Molten rock rises through cracks
It cools and forms new crust
Old crust is pulled away
Oldest crust is pulled down into trenches into
asthenosphere and destroyed. Called
• So…Sea floor is only 180 million years old
• Earth continents are 4 billion years old
Sea floor spreads because of…Convection Currents
Sea floor spreading and convection
http://Sea Floor Spreading with Bill Nye/
Divergent Boundary
• Where plates move apart
• Can form Rift Valley on land
Divergent Boundary
Example: divergent plate
boundary is the Red Sea.
Once, the Arabian peninsula and
Africa formed a single continent.
They are now being ripped apart.
The white arrows show the
directions the two plates are
moving. You can see that a new
ocean, the Red Sea is being
formed as they separate.
Convergent Boundary
• The dense, leading edge of the oceanic plate
actually pulls the rest of the plate into the
flowing asthenosphere and a subduction
zone is born! Where the two plates intersect,
a deep trench forms.
• Volcanoes and mountain ranges usually occur
along these boundaries.
• Think Ring of Fire, Swiss Alps, Appalachian
Transform Boundary
• Two plates scrape past each other
• Usually form along plate lines
Transform Boundary
• Example of Transform Boundary would be the
San Andreas Fault in California
• Earthquakes usually happen along transform
Magnetic Reversals
http://Video explanation of sea floor spreading
and magnetic reversals