Key Observations
What did Alfred Wegener first propose about continents?
Continents were once joined in a single landmass and drifted apart over time.
What are the three major types of plate boundaries?
Divergent, convergent, and transform.
What does the term "Pangea" mean?
"All lands."
What is seafloor spreading?
The process where new oceanic crust forms at mid-ocean ridges and pushes older crust outward.
What is the average thickness of continental crust?
About 30-50km.
Name one piece of evidence Wegener used to support his theory.
Fossil distributions, matching rock formations, glacial striations, or the fit of continental coastlines.
What happens at a convergent boundary involving oceanic and continental plates?
The denser oceanic plate subducts beneath the continental plate, forming volcanic mountain ranges.
Approximately how many years ago did Pangaea exist?
About 300 million years ago.
How does magnetic striping provide evidence for plate tectonics?
Reversed polarity stripes show Earth's magnetic field flips and new crust forms symmetrically at ridges.
How does the density of oceanic crust compare to continental crust?
Oceanic crust is denser.
How do glacial striations support the idea of continental drift?
They show glaciers once moved across continents now far apart, indicating past different positions.
Describe the geological features formed at divergent boundaries.
Mid-ocean ridges, rift valleys, and new oceanic crust.
What major geological event occurred as Pangaea began to break apart?
Continental drift and the opening of new oceans.
Describe how the age of oceanic crust varies with distance from mid-ocean ridges.
Crust is youngest at the ridge and gets older farther away.
Why is oceanic crust generally younger than continental crust?
It is constantly formed at ridges and destroyed at subduction zones.
What type of fossil did Wegener find on multiple continents that supported his theory?
Mesosaurus fossils.
What is a transform boundary and what geological activity is associated with it?
Plates slide past each other horizontally, causing earthquakes.
Name one modern-day continent that was once part of Pangaea.
Africa, South America, North America, Europe, Asia, Antarctica, Australia
What geological features are created when plates slide past each other?
Faults and earthquakes.
Describe the process of crust formation at mid-ocean ridges.
Magma rises, cools, and solidifies to create new oceanic crust.
Describe how matching rock formations across continents indicates a shared geological history.
Identical rock layers on separate continents show they were once connected.
Explain how subduction leads to volcanic arcs.
The subducting plate melts, and rising magma creates chains of volcanoes on the overriding plate.
How does the theory of Pangaea explain current continental shapes?
Continents fit together like puzzle pieces and share fossils and rock formations.
How do scientists determine the rate of plate movement?
By measuring the age of rocks, magnetic striping, and GPS tracking.
Explain how the characteristics of oceanic and continental crust affect tectonic activity.
Oceanic crust is thin and dense (subducts easily), while continental crust is thick and less dense (resists subduction).