Lesson 15 Plate Tectonics Flashcards
What was the main objection to Wegener’s proposal?
its inability to provide a mechanism for the movement of continents
When did Alfred Wegener first proposed his hypothesis?
1915
What did Afred Wegener publish with his hypothesis ?
The Origin of Continents and Oceans
Who discovered ideas about continental drift: an idea before its time?
Afred Wegener
Wegener’s continental drift hypothesis said that a super continent called _______ began breaking apart into smaller pieces how many years ago?
Pangaea
200 million
What was Pangaea considered?
super-continent
The smaller continental fragments that broke off then “drifted” to their _______. Continents “broke” through the ______
present positions
ocean crust
What evidence did wegener use to support the idea that continents were once joined?
Fit of South America and Africa
Fossils match across the seas
Rock types and structures match
Ancient climates
The theory of plate tectonics is a far more _______ theory than continental drift?
encompassing
What occurs along the dynamic margins of these plates?
Most of Earth’s seismic activity, volcanism, and mountain building
What is Earth’s rigid outer shell?
lithosphere
What does the plate tectonics theory say the lithosphere contains?
7 plates
What is the movement of the lithosphere plates?
moving slowly and relative to each other
Where are most of the lithosphere plates found?
beneath the ocean
What is the largest lithosphere plate?
Pacific plate
What allows for the motion of he lithosphere?
Asthenosphere
What is the temp and strength of the asthenosphere compared to the lithosphere?
Hotter and weaker than lithosphere
Where does the asthenosphere exist?
beneath the lithosphere
A major departure of the plate tectonics theory from the continental drift hypothesis is that large plates contain both __________ and the entire plate moves.
continental and ocean crust
Where do all major interactions among plates occur?
along their boundaries
In continental drift, Wegener proposed that the _______ continents “drifted” by breaking through the oceanic crust, much like ice breakers cut through ice.
sturdier
What are the types of plate boundaries?
divergent
convergent
transform fault
What boundary happens when two plates move apart?
Divergent plate boundaries
When divergent plat boundaries form, what upwells to create what?
mantle upwells creating a new seafloor
Where do divergent boundaries occur?
along the axis of the oceanic ridges
What are divergent boundaries associated with?
seafloor spreading
Where do continental rifts form?
spreading centers within a continent
New divergent boundaries may form within a continent. Give example?
the East African Rift Valleys
What is the normal spreading rate of the seafloor?
5 to 9 cm per year
2 to 15 cm per year
What does divergent plate boundaries have?
constructive margins
Where do oceanic ridges develop?
well-developed boundaries
How much of the earths surface do oceanic ridges represent?
20 percent
What may develop along the axis of oceanic ridges?
Rift valleys
What are controlled by spreading rates of the seafloor?
Topographic differences
What were plate tectonics considered?
the new paradigm
When new divergent boundaries form within a continent, they fragment a ______ and develop a new ________
landmass
ocean basin
