Tectonic Plates Flashcards
What did Alfred Wegner do?
He noticed South America and Africa appeared to fit together. He wondered if the two continents were once joined and then moved apart. He set out to find evidence to support or refute this idea. His continental drift hypothesis’ evidence was that the continents appear to fit together, if the continental margins are included, the fit is even better.
What is evidence for continental drift?
Rocks of the same type and age were on both sides of the Atlantic Ocean. Mountain ranges looked connected across the Atlantic Ocean. The evidence left by some ancient glaciers is very close to the equator. Wegener discovered ancient coal seams and coral reef fossils in areas that are much too cold today.
What’s Pangea?
Around 300 million years ago, the continents had all been joined, creating the supercontinent Pangaea. The supercontinent later broke apart, and the continents have been moving into their current positions.
What’s Magnetic Polarity?
Earth’s magnetic field surrounds the planet from pole to pole. Magnetite crystals, line up with Earth’s magnetic field as lava cools. Anywhere lava has cooled, they point to the magnetic poles. Scientists said that the poles were fixed but the continents moved. They named the phenomenon apparent polar wander.
What were echo sounders?
During World War II, battleships and submarines had echo sounders. Their goal was to locate enemy submarines Echo sounders produce sound waves that travel in all directions. The sound waves bounce around and return to the ship. Scientists can calculate the distance to the object that the sound wave hit. Most sound waves didn’t hit submarines. Instead, they were used to map the ocean floor.
What was mapped by echo sounders?
Mid-ocean ridges, (A chain of mountains rising above the seafloor)
rift zones, (In the middle of the mid-ocean ridges is a rift zone)
deep sea trenches,
abyssal plains, (Flat areas that may be dotted with volcanic mountains)
guyots, (Flat topped mountains)
continental margin (The transition from the land to the deep sea)
What are magnetic stripes?
There are stripes with different magnetisms surrounding mid-ocean ridges. Some stripes have normal polarity and some have reversed polarity. The magnetic stripes end at the edges of continents.
Where is the seafloor youngest and oldest?
The seafloor is youngest at the ridge crest and oldest is far away from the ridge crest.
What is mantle convection?
Convection currents in the mantle that create sea-floor spreading.
What did Harry Hess do?
Hess published a new idea that he called seafloor spreading. He wrote that hot magma rises up into the rift valley at the mid-ocean ridges and the lava cools to form new seafloor. When more lava erupts at the ridge, the new lava pushes the seafloor horizontally away from the ridge axis
What’s the aesthenosphere?
Part of the earths upper mantle that is solid but can flow.
What can tectonic plates be made of?
Oceanic or continential lithosphere. Their outlines can be seen by the locations of earthquake epicentres.
What’s an epicentre?
The point on Earth’s surface directly above the place where an earthquake occurs.
Why is there convection currents in the mantle?
Mantle material is heated above the core, and rises towards the surface. As the mantle rises, it cools. At the surface, the material moves horizontally away from a mid-ocean ridge crest and sinks back down. This proccess repeats.
Where do 2 plates meet?
At a divergent, convergent, or transform plate boundary.
What does plate tectonic theory explain? (6)
- Earth’s geography changing
- earthquake prone regions
- volcanic eruptions
- mountain ranges locations
- ore deposits location
- living and fossil species of plants and animals locations
What do plates do at a divergent boundary?
Plates move apart at mid-ocean ridges and continental rift zones. Crust is created.
What’s continental rifting?
Magma rises beneath the continent, causing it to become thinner, and split apart. New ocean crust erupts in the void, creating an ocean between continents.
What is a transform boundary?
2 plates sliding past each other in oposite dirrections. The plates meet at a transform vault. They have HUGE earthquakes. Crust is neither created or destroyed.
