What is Pangaea?
The name given to a supercontinent
that broke apart into today’s
continents
Who was Alfred Wegener?
The scientist who formulated the
continental drift hypothesis
State the continental drift hypothesis.
Continents are in constant motion on
the surface of the Earth.
Which way do compasses point when
Earth’s magnetic field is “normal”?
Which way when it is “reversed”?
Normal – north
Reversed – south
Where does seafloor spreading take
place?
Along mid-ocean ridges
What is a mid-ocean ridge?
Mountain ranges in the ocean created
by the rising of magma through Earth’s
crust
How does the age of the ocean floor at The ocean floor near the mid-ocean
the mid-ocean ridge compare to the
ridge is younger than the ocean floor
age of the ocean floor near a
near a subduction zone
subduction zone?
How do scientists know that the
Earth’s magnetic field has reversed
direction during geologic history?
Describe the process of seafloor
spreading.
Why was Wegener’s hypothesis not
accepted by other scientists during his
time?
The igneous rock (basalt) contains iron
that solidifies in the direction of the
Earth’s magnetic field. Scientists have
read the magnetic signatures of rocks
at different distances from the midocean ridges and seen that they were
oriented in different directions.
Seafloor spreading occurs when
magma rises through cracks in the
oceanic crust along the mid-ocean
ridge. The lava cools forming rock
called basalt. As magma continues to
rise and solidify, it pushes away the
newly formed crust from the midocean ridge.
Wegener did not have a way to explain
the process or forces that could have
caused the continents to move.
Describe a convergent plate boundary. Where two tectonic plates collide
Describe a divergent plate boundary.
Where two tectonic plates separate
What is a subduction zone
The area where a denser tectonic plate
descends into Earth along a
convergent plate boundary
Fossils
List the three main clues that Wegener Climate
used to develop his hypothesis of
Rock
continental drift?
How did Wegener use fossils as
evidence of continental drift?
He saw that fossils of the same animals
existed on different continents
separated by oceans, suggesting the
land was once connected and drifted
apart
How did Wegener use rocks as
evidence of continental drift?
He saw that mountain ranges and rock
formations had common origins but
are located in different parts of the
world, suggesting that the land was
once connected but moved apart
Describe an abyssal plain
A flat area of accumulated sediment
on the ocean floor that is far from the
mid-ocean ridge
What are magnetic bands on the
ocean floor?
Areas of alternating rock evidence of
normal and reverse polarity.
How do continents move on Earth?
Continents move with the oceanic
crust as the seafloor spreads along the
mid-ocean ridge
What is permanently recorded in the
basalt at the seafloor?
The strength and direction of Earth’s
magnetic field.
What type of rock is commonly found
on the ocean floor?
Explain the term “magnetic reversal”.
An igneous rock called basalt
When a magnetic field reverses
direction
What do you call a state in which
magnetized objects reverse direction
and orient themselves to point south?
Reversed polarity
Approximately how long ago do
scientists think Pangaea existed?
About 250 million years ago
Explain how Wegener used the shapes
of the continents to support his
hypothesis of continental drift.
Wegener said that the continents fit
together like the pieces of a puzzle.