Continental Drift Hypothesis
100 years ago, Alfred Wegener proposed that all the continents were once part of a supercontinent. What is the name of that supercontinent?
Pangea
What tool do scientists use to determine how deep the ocean is at any given place?
Thye use echo-sounders
True or False: All of Earth's tectonic plates are roughly the same size.
False
Over time, _________ began breaking apart, and the continents started moving to where they are now.
Pangea
Below the lithosphere is the ___________, which is so hot that it flows like plastic.
asthenosphere
Who first proposed the hypothesis of continental drift?
Alfred Wegener
Sea-floor spreading occurs at mid-ocean ridges. Is new oceanic crust formed closest to mid-ocean ridges, or far away from mid-ocean ridges?
New oceanic crust is formed closest to the mid-ocean ridge
Name the 3 types of plate boundaries
Convergent, divergent, transform
Fossils of ancient plants and animals, as well as coal deposits in Antarctica, provide evidence for continental ____.
drift
When two plates collide, a ____________ plate boundary forms.
convergent
Name all 7 continents
Europe, Africa, Asia, North America, South America, Australia, Antarctica
Which is more dense, continental crust or oceanic crust?
Ocean crust is more dense
What forms when 2 continental plates collide?
The plates are pushed up and fold and form tall mountain ranges.
After a _________________, a magnet points south because Earth’s magnetic field has reversed polarity.
magnetic reversal
The three forces that interact to cause tectonic plate motion are ________, basal drag and slab pull.
ridge push
Ridge push is a force that results when a mid-ocean ridge is higher than the surrounding land, allowing gravity to pull down on the rocks and cause plates to move away from the ridge.
Define Rift.
A rift is a large crack or opening in the earth's crust.
How often do magnetic reversals occur?
Every few hundred thousand to every few hundred million years
What are the 2 main factors that cause convection?
Differences in density and temperature cause convection.
Earth's internal thermal energy causes the mantle to heat, expand and rise. When it reaches the crust, the hot mantle cools and becomes denser, and sinks, forming convection currents.
____________________ helps explain continental drift because it shows that continents move with the oceanic crust as it spreads away from mid-ocean ridges.
Seafloor spreading
The area where a denser plate descends into Earth along a convergent plate boundary is called a ___________ zone.
subduction
Why did Alfred Wegener's colleagues question the continental drift theory?
Because it was a slow process and it was not possible for Wegener to measure how fast the continents moved. Also, Wegener could not explain the forces that caused the continents to move.
How are mid-ocean ridges and an abyssal plain topographically different?
Mid-ocean ridges are mountains on the seafloor with a rift valley between them. The abyssal plain is the flat area of the seafloor where the sediment collects.
Contrast the lithosphere and the asthenosphere.
The lithosphere is thin and rigid and is made of the crust and the solid upper mantle. The asthenosphere is thick and behaves like plastic. The asthenosphere is part of the mantle.
The cold, rigid rock layer on the outermost part of Earth is called the __________. It consists of crust and the upper part of the mantle
lithosphere
When a plate is undergoing ____________, a cold, dense slab of rock sinks into the mantle along a subduction zone. As it sinks, the slab pulls the rest of the plate down into the mantle.
slab pull
When a plate is undergoing slab pull , a cold, dense slab of rock sinks into the mantle along a subduction zone. As it sinks, the slab pulls the rest of the plate down into the mantle.