Answer Sheet
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Earth Science 3a: Ocean floor patterns
The magnetic stripes of the ocean floor are evidence of the earth’s magnetic field
reversing polarity. They are also evidence of continental drift. The age of the ocean
floor is newer near a ridge and older far away from a ridge.
On unit III we talked about electricity and magnetism. In this unit we saw a movie about
the Earth’s magnetic field. I learned that the Earth’s magnetic field reverses polarity
about every 800,000 years. Without a magnetic field the Earth would be exposed to
radiation. Good thing the outer core is liquid and not solid!!!
Ocean crust is created at a ridge and destroyed at a trench.
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Earth Science 3b: Plate boundaries
Oceanic crust is denser than continental crust. This is important because the denser crust
will subduct under the less dense crust. Oceanic crust is made out of basalt, while
continental crust is made out of granite.
The three types of plate boundaries are convergent, divergent and transform.
At convergent boundaries two plates collide into one another. At divergent boundaries
two plates move away from each other. At transform boundaries two plates slip past one
another.
An oceanic ridge is formed by two oceanic divergent boundaries. At this type of
boundary crust is created. At a ridge crust is very thin.
A trench is formed by a continental crust and an oceanic crust. At a ridge the two
boundaries are diverging. At this type of boundary oceanic crust is destroyed. At a
trench crust is very thick.
A soft -focus earthquake is formed at a transform boundary and a deep-focus earthquake
is formed at a convergent boundary.
Mountains are formed by two continental converging plates, while rift valleys are formed
by two continental diverging plates.
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Earth Science 3c:Rocks
The three types of rocks are igneous, sedimentary, and metamorphic.
Igneous rocks are formed by magma cooling. There are two sub-categories of this type
of rock, they are plutonic and volcanic. The extrusive ones cool fast therefore it has very
small crystals. The intrusive ones cool slowly therefore it has very large crystals. You
can find this type of rock at divergent boundaries because magma rises and cools at this
type of boundary.
Sedimentary rocks are formed by weathering and deposition. The texture is very rough.
Anthropologists are specially excited to be around this rock because you can find fossils
embedded in it!!!!!
Metamorphic rocks are those that get transformed by heat and pressure. Thee rocks have
many layers and are very dense. You can find this type of rock at a oceanic-continental
convergent boundary because a plate subducts into the mantle increasing the pressure and
temperature of the rocks.
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Earth Science 3d:Earthquakes
Earthquakes are mechanical waves therefore they carry energy from one place to another.
The waves bend when going through the layers of the earth, a wave characteristic called
refraction ( the bending of waves due to a change in medium). This is what allows
scientist to study the structure of the Earth!!!!
The two type of Earthquake waves are P-type and S-type. The P-type is longitudinal
while the S-type is transverse.
A seismograph is an instrument used to measure the motion of the ground.
The Richter scale measures the magnitude of an earthquake. It measures the amplitude of
the wave, therefore measuring the energy of a wave ( hint: remember that E=A2) An
Earthquake with magnitude 5.0 releases 10 times more energy than a 4.0 magnitude.
And 10*10=100 times more energy than a 3.0 magnitude.
The Mercalli scale measures the intensity of an earthquake. An earthquake of intensity
6.0 has 30 times more intensity than a 5.0.