Chapt. 9

What was the same of the super-continent?
Pangaea, meaning “all land”
What did Wegener argue must have once been joined based on fossils?
South America and Africa must have been joined.
What does rock evidence exist in the form of?
Rock evidence for continental drift exists in the form of several mountain belts that end at one coastline, only to reappear on a landmass across the ocean.
Where were areas of glacial till found?
Layers of glacial till were found in southern Africa and South America, as well as India and Australia.
What could Wegener not describe?
A mechanism that was capable of moving the continents across the globe.
What is the new theory known as?
Plate tectonics.
What are the segments of the lithosphere called?
Plates
What is the movement driven by?
The unequal distribution of heat within Earth
What are also called spreading centers?
Divergent boundaries
What happens at convergent boundaries?
Two plates move together.
What is an example of a transform plate boundary?
Transform boundaries are margins where two plates grind past each other without the production or destruction of the lithosphere.
What two things continuously add oceanic lithosphere?
Spreading and upwelling of magma continuously adds oceanic lithosphere.
What is the longest physical feature on Earth’s surface?
The system of ocean ridges is the longest physical feature on Earth’s surface.
What is the process by which new oceanic lithosphere is produced?
Seafloor spreading is the process by which plate tectonics produces new oceanic lithosphere.
What are subduction zones?
Destructive plate margins where oceanic crust is being pushed down into the mantle are called subduction zones.
What two things control convergent boundaries?
1. type of crust
2. forces acting on plate
What happens when two oceanic slabs converge?
One descends beneath the other. Cuaes volcanic activity similar to what occurs at an oceanic-continental boundary. Volcanoes form in the ocean instead of on land. New land consisting of an arc shaped chain of small islands called a volcanic island arc.
What happens at transform plate boundaries?
Plates grind past each other without destroying the lithosphere
Where are most transform plate boundaries located?
Within the ocean basins, but few cut through the continental crust. Ex. San Andreas Fault (California)
What is normal polarity?
When rocks show the same magnetism as the present magnetic field
What is the strongest evidence of sea-floor spreading?
The discovery of strips of alternating polarity, which lie as mirror images across the ocean ridges
What close link is obvious?
Scientists found a close link between deep-focus earthquakes and ocean trenches. Also, the absence of deep-focus earthquakes along the oceanic ridge system was shown to be consistent with the new theory.
What was the drilling ship used from 1968 to 1983 named?
Glomar Challenger
What is the basic driving force for plate movement?
Convection occurring in the mantle is the basic driving force for plate movement