“Continental Drift and Plate Tectonics Study Guide”
ANSWERS:
1. Explain 4 types of evidence that Alfred
Wegener used to explain continental drift. Some
continents look like they fit together (exampleS. America & Africa), Geological Clues (Ex.
Mountain Belts lined up in North America &
Europe), Fossil Clues (Ex. Mesosaurus found in
S.America & Africa. Glossopteris found in S.
America, India, Africa, & Antarctica),Climate
Clues (Glacial deposits in tropical regions like
India and Australia.)
2. Completely explain seafloor spreading and how
scientists know it is happening. The theory
states that magma travels to the earth’s surface.
The magma forms cracks in the ocean floor.
The magma pushes out of the cracks. Magma piles
up and forms mid-ocean ridges. As the magma
hardens it pushes the layers of the ocean floor
away from the mid-ocean ridge. The process then
repeats it self.
Proof- The existence of pillow lava (on sea
floor), the oldest layers of the Atlantic Ocean
floor are on the coastline of the continents.
(180 million years old.) The youngest layers of
the Atlantic Ocean floor are in the center of the
ocean (50 million years old). Magnetic reversals
can also be used as seafloor spreading proof.
Every 200,000 years or so, the earth’s poles
reverse. During those times any rock that forms
will have a record of what the polarity was at
that time. Since the polarity of the rock that
makes up the ocean floor changes, the ocean floor
rock must have formed at different intervals.
This would have moved the existing rock away from
the center as new rock formed. If seafloor
spreading did not take place the whole ocean
floor would have the same polarity.
3. Completely explain what plate tectonics is and
how it works.
Plate tectonics is the theory that earth’s
lithosphere is broken into sections, called plates,
that slowly move around on the asthenosphere.
Convection of magma is the driving force that makes
the plates move. Material close to the core is hot
and has a low density. Material close to the
surface is cooler and has a high density. The more
dense material sinks and the less dense material
rises. Because magma is sticky, when the magma
reaches the plates it pushes or pulls the plates
toward or away from a boundary.
4. Why do plates move?
Plates are less dense than the asthenosphere is.
This allows them to float on top of the
asthenosphere and be moved easily by the seafloor spreading and (convection currents).
5. Why does earth have land features like the
ones we talked about in class?
Volcanoes can be found at any divergent boundary,
an ocean-ocean plate convergent boundary, and a
continental plate ocean plate convergent
boundary. Mountains form when two continental
plates collide. Neither plate is dense enough to
sink so you do not have any eruptions. A rift
valley forms when any two plate separate. 2 other
features are found inside of a rift valley.
Volcanoes can be found there due to the rising
magma. Ridges or mid-ocean ridges could also be
found there due to the magma coming out of the
ocean floor cracks. Trenches form at the base of
a continental ocean plate boundary and an ocean
plate ocean plate boundary because the more dense
plate of the two sinks forming a deep v-shaped
valley.
6. What are the layers of the EARTH and how are
they different from one another? Are any of them
similar? Earth has 4 basic layers, crust, mantle,
the outer and inner cores.
Specific sub-layer
would be the lithosphere (crust and topmost
mantle) and the asthenosphere (upper mantle).
Each layer has differing densities, temperatures
and thicknesses.
Most layers have slightly
different compositions, though some elements are
found throughout all the layers. These elements
would be similarities. Also the fact that all
layers are fairly solid except for the outer
core.
7.
How we know how deep layers are and what they
are made of if we have never been there? What
is the *Mohorovicic discontinuity?
Scientists have used 2 types of evidence to
learn about the Earth’s interior, rock
samples (direct evidence) and seismic wave
behavior(indirect evidence).
Drilling holes
and look at samples and studying cooled magma
from the interior helps scientists determine
the make up of the interior.
Scientists
observe the waves generated by earthquakes.
They study the changes in speed and path of
the waves as they travel through the interior
and can determine differing densities and
compositions and certain depths.
The "Moho",
is the boundary between the crust and the
mantle--- The Mohorovicic Discontinuity marks
the lower limit of Earth's crust.
At this
depth seismic waves change velocity. At this
discontinuity, seismic waves accelerate due
to density increase of the material.