Pangea
A single large land mass containing all current land masses.
When did Pangea form?
245 million years ago.
Panthalassa
The single large ocean surrounding Pangea.
When did Pangea break into 2 land masses?
200 million years ago.
What were the two land masses called?
Laurasia and Gondwala.
What evidence supports continental drift?
1) Fossils of same species are found on continents separated by Atlantic Ocean.
2) Mountain ranges on edges of continents separated by ocean formed at the same time.
What formed in the rift when Laurasia broke apart?
The North Atlantic Ocean.
What did Laurasia break up into?
North America and Eurasia.
In which direction did Laurasia drift?
Laurasia drifted North when it broke from Pangea.
What did Gwondala break into?
Gwondala broke into 2 land masses. One contained South America and Africa. The other contained Antarctica, Australia and India.
When did Africa and South America split?
150 million years ago.
What formed when Africa and South America split?
The South Atlantic Ocean.
When did India, Australia and Antarctica split?
150 million years ago.
When India broke from Australia and Antarctica, what direction did it move?
India moved North.
When did India collide with Eurasia?
50 million years ago.
What formed when India collided with Eurasia?
The Himalayan Mountains.
Why was Wegener's ideas of continental drift ignored for years?
Because scientists could not determine how continents moved?
When were the mid-ocean ridges found?
In the mid 1900s when scientists began mapping the sea floor.
What are mid-ocean ridges?
Huge under-water mountain ranges.
What theory did the discovery of mid-ocean ridges lead to?
Plate tectonics
What did the theory of plate tectonics build on?
Some of Wegener's ideas.
Where do mid-ocean ridges form?
Along cracks in the crust.
Where are the youngest rocks located according to rock samples?
Closest to the mid-ocean ridge.
Which is older, the oldest ocean crust or the continental crust?
The continental crust is older.
Sea floor rock contains what kind of patterns
Magnetic patterns.
How are the magnetic patterns on each side of the ridge similar?
They are mirror images of each other.
What is sea floor spreading?
A process proposed by scientists to explain the age and magnetic patterns of sea-floor rocks.
What forms new ocean crust?
Molten rock from within the Earth rises through the cracks in the ridges and cools.
How does the sea floor spread?
When molten rock rises, the old crust breaks along the mid point of the ridge and the two pieces of the ocean floor move in opposite directions.
As the sea floor moves...
so do the continents on the same piece of crust.
If the sea floor has been spreading, why is the earth not getting larger?
There are huge trenches, like deep canyons, in the sea floor, where the dense oceanic crust is sinking into the asthenosphere. This causes the earth to remain the same size.
What are the two components of continental drift?
sea-floor spreading and ocean trenches
Plate tectonics
the theory which explains the large scale movements of Earth's lithosphere.
Tectonic plate
A tectonic plate is a piece of the lithosphere which moves around on top of the asthenosphere and fits together with the plates around it.
What are the major tectonic plates?
The nine major tectonic plates are the Pacific, North American, Nazca, South American, African, Australian, Eurasian, Indian and Antarctic.
Do all tectonic plates have both oceanic and continental crust.
No, the Nazca plate has only oceanic crust.
Tectonic plates cover the surface of the...
asthenosphere
Which displaces (moves) more of the asthenosphere, continental or oceanic?
Continental, because they are thicker, even though oceanic is more dense than continental.
Which is the thickest part of the South American plate, the continental crust or the Atlantic Ocean?
The continental crust.
Where do the most dramatic changes in the Earth's crust occur?
Along plate boundaries.
Where can the plate boundaries occur?
On the ocean floor, around the edges of continents, or even within continents.
What are the three types of plate boundaries?
Divergent boundaries, convergent boundaries, transform boundaries.
What is each type of plate boundary associated with?
Characteristic landforms.
Convergent boundaries
Form where two plates collide.
What are the three types of collision that can occur at convergent boundaries
Continent-Continent Collision, Continent-Ocean Collision, Ocean-Ocean Collision.
What happens in a Continent-Continent Collision?
The plates buckle and thicken which pushes some of the continental crust upward (forming mountains).
What happens in a Continent-Ocean Collision?
The oceanic plate subducts (goes under the continental plate) because the oceanic plate is denser.
What happens in a Ocean-Ocean Collision?
The older, denser oceanic plate subducts (goes under the new lighter oceanic plate).
Divergent boundaries
Where two plates move away from each other.
Why does the denser plate subduct in a collision of tectonic plates?
because it is heavier and gravity pulls it down more than the less dense plate.
What does a divergent boundary allow?
The separation of a divergent boundary allows the athenosphere to rise toward the surface and partially melt.
What does the melting asthenosphere create?
Magma, which erupts as lava and then cools and hardens to form new rock on the ocean floor.
As the crust and the upper part of the asthenosphere cool and become rigid...
they form new lithosphere.
Newly formed lithosphere is...
thin, warm and light.
Where does the warm, light rock sit with respect to the ocean floor?
It sits higher than the surrounding sea floor because it is less dense.
What does the warm, light newly formed rock form?
Mid-ocean ridges.
Most divergent boundaries are located where?
On the ocean floor.
Rift valleys may also form...
where continents are separated by plate movement.
Transform boundary
A boundary where two plates move past each other.
Do transform boundary plate edges slide along smoothly?
No, they scrape against each other in a series of sudden slippages which are felt as earthquakes.
Do transform boundaries produce magma?
No, transform boundaries do not usually produce magma.
What type of boundary is the San Andreas fault?
A transform boundary.
What two plates form the San Andreas fault?
North American plate and the Pacific plate.
Where else does transform motion occur?
It also occurs at divergent boundaries.
What are fracture zones?
They are transform faults which connect short segments of mid-ocean ridges.
How are transform boundaries different from convergent and divergent boundaries?
At transform boundaries, plates move past each other horizontally.
What are the three proposed mechanisms to explain how tectonic plates move over the Earth's surface?
Mantle Convection, Ridge Push, Slab Pull
Mantle Convection
Plates are dragged along as the mantle material moves beneath the tectonic plates.
Convection
Movement of material due to differences in density.
What is the criticism of Mantle Convection?
It does not explain the huge amount of force needed to move plates.
What causes the mantle material to be heated?
As atoms in the Earth's core and mantle undergo radioactive decay, energy is released as heat and some parts of the mantle become hotter than others.
Ridge Push
As newer lighter rock located on top of the ridge cools and becomes more dense, gravity pulls it down, the slope, pushing the plate away from the mid-ocean ridge.
Slab Pull
The leading edge of the subducting plate is more dense than the mantle. This causes it to sink into the mantle and pull the rest of the plate in its direction.
Do subducting plates move faster or slower than other plates?
They move faster than other plates.
Why do scientists believe that Slab Pull may be the most important mechanism in driving tectonic plate motion?
Because subducting plates move faster than the other plates.
What do scientists call the continent where all land masses were joined together as one.
Pangea.
The United States lies on what plate?
The North American plate.
In what plate boundary type do land masses slide past each other horizontally?
Transform Boundaries.
What are the three mechanisms that may drive plate motion?
Mantle Convection, Slab Pull, Ridge Push
Which mechanism driving plate motion do scientists feel is the most important?
Slab Pull
The lithosphere is divided into pieces called...
Tectonic Plates
The theory that describes large scale movements of the Earth's lithosphere is called...
Plate Tectonics.
The movement of material due to differences in density that are caused by differences in temperature is called...
Convection
Which types of lithosphere take part in convergent collisions?
Continental Crust
What land forms are likely to form at convergent collisions?
Mountain ranges.
How is continental lithosphere different from oceanic lithosphere?
Continental lithosphere is thicker tan oceanic lithoshpere.
How are convergent boundaries different from divergent boundaries?
Convergent boundaries are where plates collide or move towards each other, divergent boundaries are where plates are pulling apart or forming rifts.
What does cool rock sink when convection takes place in the mantle?
Cool rock is more dense than the surrounding hot, ligher mantle material, and thus sinks.