Plate Tectonics Flashcards
Who is credited with developing the continental drift hypothesis?
Alfred Wegener
What was the first line of evidence that led early investigators to suspect that the continents were once connected?
the coastlines of some continents fit together like pieces of a jigsaw puzzle.
What was Pangea?
, a supercontinent that incorporated almost all the landmasses on Earth.
Describe the four kinds of evidence that Wegener and his supporters gathered to substantiate the continental drift hypothesis?
fit of the continents, paleoclimate indicators, truncated geologic features and fossils.
Explain why the discovery of the fossil remains of Mesosaurus in South America and Africa, but nowhere else, supports the continental drift hypothesis.
Mesosaurus couldn’t have crossed an ocean between the two continents which suggests that the continents were connected.
Early in the 20th century, what was the prevailing view of how land animals migrated across the vast expanse of open oceans?
rafting, transoceanic land bridges, and island stepping.
How did Wegener account for the existence of glaciers in southern landmasses at a time when areas in North America, Europe, and Asia supported lush tropical swamps?
suggesting that the southern continents were joined together and located near the South Pole to provide the conditions necessary for large glaciations.
To which two aspect of Wegener’s continental drift hypothesis did most Earth scientists object?
His inability to identify a credible mechanism for continental drift and his suggestion that larger and sturdier continents broke through thinner oceanic crust like ice breakers cut through ice.
What is meant by seafloor spreading? Who is credited with formulating this important concept? Where is active seafloor spreading occurring today?
Molten material wells up into the fractures created by the seafloor spreading and creates new oceanic crust.
This concept was proposed by Harry Hess.
Describe how Fred Vine and D.H. Mathews related the seafloor spreading hypothesis to magnetics reversals.
They hypothesized that the reverse polarized rocks formed at the ridges during the geologic past when the earth’s magnetic field had reverse
Compare and contrast the lithosphere and asthenosphere.
Both the lithosphere and asthenosphere are part of Earth and are made of similar material.
Lithosphere is made up of Earth’s outermost layer while the asthenosphere is the middle layer of Earth.
List three types of plate boundaries and describe the relative motion at each of them.
Divergent boundaries – where new crust is generated as the plates pull away from each other.
Convergent boundaries – where crust is destroyed as one plate dives under another.
Transform boundaries – where crust is neither produced nor destroyed as the plates slide horizontally past each other.
Where does new lithosphere form? Where is it consumed? Why does the rate at which new lithosphere forms roughly balance the rate at which lithosphere is destroyed?
New lithosphere is constantly being produced at the oceanic ridges.
Lithosphere is consumed at the subduction zones.
A balance is maintained because older, denser proportions of oceanic lithosphere descend into the mantle at a rate equal to seafloor production.
Briefly describe the process of continental rifting. Where is it occurring today?
Mantle plumes beneath continental crust generate magmatic upwelling and forces that pull the crust apart, generating a new rift valley. The rift valley eventually widens to create a new ocean basin.
It is occurring today in East Africa.
Compare a continental volcanic arc and a volcanic island arc.
The magma produced in continental volcanic arc is more silica rich than that formed at a volcanic island arc.
Why does oceanic lithosphere subduct while continental lithosphere does not?
The oceanic lithosphere is denser than the continental lithosphere
Briefly describe how mountain systems like the Himalayas are formed.
two large landmasses, India and Eurasia, driven by plate movement, collided.
Differentiate between transform faults and the two other types of plate boundaries.
At divergent plate boundaries, new oceanic crust is formed. At convergent boundaries, old oceanic crust is destroyed. But at transform plate boundaries, crust is neither created nor destroyed.
Some people predict that some day California will sink into the ocean. Is this idea consistent with the theory of plate tectonics?
No. California’s bedrock is continental crust and will not subduct in oceanic crust
With which of the three types of plate boundaries are the following places or features associated: Himalayas, Aleutian Islands, Red Sea, Andes Mountains, San Andreas Fault, Iceland, Japan, Mount St, Helens.
Convergent and Divergent
What is the age of the oldest sediment recovered by deep-sea drilling? How do the ages of these sediments compare with the ages of the oldest continental rocks?
Oldest age of sediment recovered is 180 million years old. Most continental crust exceeds several hundred million years and some have been located that exceed 4 billion years.
Assuming hot spots remain fixed, in what direction was the Pacific plate moving while the Hawaiian Islands were forming? When the Suiko Seamount was forming?
The Pacific plate was moving northwest when the Hawaiian islands were forming and moving north when the Suiko Seamount was forming.
Describe slab-pull and ridge-push. Which of these force appears to contribute the most to plate motion?
A slab pull is the strongest mechanism that contributes to plate tectonic motion and is a force generated by gravity acting on dense oceanic plates subducting into the mantle.
What role are mantle plumes thought to play in the convective flow of the mantle?
Mantle plumes are the likely cause of “hot spots”
Briefly describe the two models for mantle-plate convection. What is lacking in each of these models?
Whole mantle convection - convection may occur throughout the entire mantle
Layer Cake Model - it may only occur in two layers within the mantle (upper and lower)
