Transcript Plate Tectonics

Plate Tectonics
Continental drift
• All continents were once connected as
one large landmass called Pangaea.
• Landmass broke apart and drifted to their
present positions.
Evidence for continental drift
• Puzzle-like fit of the continents
• Similar fossils have been found on
different continents.
• Remains of warm weather plants found in
arctic areas and glacial deposits found in
tropical areas.
• Similar rock structures are found on
different continents.
Seafloor Spreading
• Mid-ocean ridges- underwater mountain
ranges discovered using sound waves.
• The theory of Seafloor spreading (Harry
Hess) explained these ridges.
1. Hot, Less dense material below Earth’s
crust rises upward to the surfaces at the
mid ocean ridges.
2. Then, it, flows sideways, carrying the
seafloor away from the ridge.
3. As the seafloor spreads apart, magma
moves up and flows from the cracks,
cools, and forms new seafloor.
Evidence for SFS
• Youngest rocks are located at mid-ocean
ridges.
• Reversal of Earth’s magnetic field are
recorded by rocks in strips parallel to
ridges.
Discussion Question
How could seafloor spreading be related to
continental drift?
Answer
• If the Seafloor is constantly spreading
apart and moving, it will effect and move
the continents as well.
Theory of Plate Tectonics
• Earth’s crust and upper mantle are broken
into sections called plates, they move on a
plastic-like layer of the mantle.
• Plates and upper mantle form the
lithosphere.
• Plastic-like layer below is called
asthenosphere.
Plate Boundaries
• Divergent Plate boundaries
– Plates moving apart.
• Convergent Boundaries
– Plates moving together.
– Denser plates sink under less dense plates.
– Newly formed hot magma forced upward
forms volcanic mountains
Plates collide
• Plates crumple up to form mountain
ranges.
• Earthquakes are common
• Transform boundary
– Plates slide past one another.
– Sudden movement can cause earthquakes
• Convection inside the Earth is thought to
be the force behind plate tectonics.
• Features caused by plate tectonics
– Faults and rift valleys
– Mountains and volcanoes
– Strike- slip faults – cause of earthquakes.