Chapter 17: Plate Tectonics Flashcards
Alfred Wegner (1912) proposed a hypothesis that Earth’s continents were once joined as a single landmass
Continental Drift
What is the name of the former supercontinent?
Pangaea
What does the word “Pangaea mean?
“All the Earth”
What is some evidence of Wegener’s hypothesis?
-Similar rock types on opposite sides of the Atlantic Ocean
-Puzzle-like fit of coastlines
-Similar fossils of animals (Cynognathus and Lystrasaurus) and plants (Glossopteris)
-Evidence of vast climatic changes on some continents from the sedimentary rock (Ex: Coal found in Antarctica, Glacial deposits found in Africa, India, Australia, and South America
What were the two major flaws of Wegener’s hypothesis?
- Wegener couldn’t explain what was causing the continents to move
- Why the continents did not shatter when they moved
What is a magnetometer?
Echo-sounding device that allows for better methods of studying the ocean floor
What does echo-sounding do?
(SONAR); allows for sound waves to travel through the water and measure depth
What is a magnetometer also used for?
Used to study ocean topography as it detects the changes in magnetic fields, mapping ridges and trenches
What is a ridge and what is a trench?
Ridge: New rock; Underground mountain ranges where earthquakes and volcanism occur
Deep-Sea Trench: Old rock; Narrow, elongated depressions in the seafloor with very steep sides
Is the rock near the ocean ridge older or younger?
Younger
Is the rock far away from the ocean ridge older or younger?
Older
Are ocean floor sediments thinner or thicker near the ocean ridge?
Thinner; thickness of sediment increases with distance from the ridge
Is continental sedimentary rock thicker or is ocean floor sediment thicker?
Continental sedimentary rock is thicker
What is the study of magnetic record provided by rocks containing iron-nearing materials?
Paleomagnetism
What is magnetic reversal?
A change is Earth’s magnetic field
What is normal and reversed polarity?
Normal: Past magnetic field that is the same as today
Reversed: Opposite magnetic field than the present
What is as isochron?
Line on a map that connects points of equal age
What is seafloor spreading?
New oceanic crust is formed at ocean ridges and destroyed at deep trenches
What is magma?
Less dense material that is forced toward the crust along the ocean ridge and then fills in the gap
What is the theory of plate tectonics?
Theory that the Earth’s crust and rigid upper mantle are broken up into around 12 huge slabs called plates
What types of plate boundaries are there?
Convergent, divergent, transform
What is a divergent boundary?
Places where two tectonic plates are moving away from one another
Describe little things about divergent boundaries
-Usually have ocean ridges
-High heat and volcanism over many years
-Rift valley is a long narrow depression in the continental crust
What is a convergent boundary?
Where two tectonic plates are moving towards one another
What are the three types of convergent boundaries?
-Oceanic - Oceanic: Creates deep-sea trenches
-Oceanic - Continental: Where volcanic eruptions can form mountain chains
-Continental - Continental: Folded Mountains
What is a transform boundary?
A place where two places slide past each other
What do transform boundaries form?
Long faults
What is convection?
Transfer of thermal energy by the movement of heated matter. Heated matter rises, cooler matter sinks, forming n a convection current.
What are believed to be the driving forces in plate mass movements?
Convection currents
What can flow like soft plastic?
Asthenosphere
What sets the plates in motion?
The transfer of energy between Earth’s hot interior and cold exterior
What is the flow rate?
A few centimeters per year
What does the rising lower density part of the convection current do?
Forces the lithosphere up and sideways to split the plates (divergent boundary)
What does the downward part of the convection current do?
Forces the plates downward (Convergent boundary)
What is a ridge push?
It is thought to push plates towards the subduction zone
What is a slab pull?
Is the weight of the subductung plate pulling it into the subduction zone/
Remember this word
Glossopteris
