Earth and Space Science chapter 17 Test
What is an isochron?
a line on a seafloor map that connects points of equal age
What is the polarity of a magnetic field that has the same polarity as the present magnetic field?
a normal polarity
What is the name of Alfred Wegener's hypothesis about moving landmasses?
continental drift
What is thought to be the driving mechanism of plate movement?
convection currents in the mantle
An expedition finds a sample in the rock on the seafloor thought to be 4 million years old. What was the polarity of Earth at that time, according to the figure?
reversed
What causes the seafloor to spread?
rising magma
How are the convection currents set in motion?
slab push and ridge pull
Much of Earth's internal heat comes from ___________________
the decay of radioactive elements
A place where two plates slide laterally past each other is called a __________
transform boundary
The theory of _____ explains how ocean crust is formed and destroyed.
seafloor spreading
Rocks close to mid-ocean ridges are __________ rocks far from mid-ocean ridges.
younger than
The __________ states that Earth's crust and rigid upper mantle are broken into plates that move at different rates and in different directions.
theory of plate tectonics
What was one reason that Wegener's hypothesis of continental drift was rejected?
He could not explain where the continents had moved.
What is the study of Earth's magnetic record?
Paleomagnetism
The supercontinent from Wegener's theory of continental drift is called __________
Pangaea
According to the figure, where is an earthquake most likely to occur
along the west coast of North America
Where do tectonic plates interact?
at plate boundaries
Where are the youngest rocks on the seafloor located?
at the mid-ocean ridges
The subduction of an oceanic plate beneath a continental plate produces a(n) _____.
chain of volcanic mountains
The geologic features on the ocean floor resulted from ____.
colliding plates in the lithosphere
Places where two tectonic plates are moving away from each other are called __________.
divergent boundaries
What evidence did Wegener use to estimate the time of Pangaea's break up?
fossil data
Which element helps preserve magnetic patterns on the ocean floor?
iron
The thickness of ocean sediments that are close to a mid-ocean ridge is __________ the thickness of ocean sediments that are far from mid-ocean ridges.
less than
__________ is a device that can detect changes in the strength of the magnetic field.
magnetometer
What two topographic features of the ocean floor were discovered only with the use of sonar?
mid-ocean ridges and deep-sea trenches
The tremendous amount of heat within Earth powers _____.
plate tectonics
What evidence did Wegener use to suggest that Antarctica had once been closer to the equator?
presence of coal beds
When a divergent plate boundary forms on continents, a __________ forms.
rift valley
Which type of information was NOT collected by Wegener to support his continental drift hypothesis?
seafloor magnetic data
Wegener proposed that the continents were __________
slowly sinking into the ocean floor
What is the process called when one plate is forced beneath another at a convergent plate boundary?
subduction
According to the data shown in the figure, what was Earth's magnetic polarity like 5 million years ago?
the reverse of today
Identify the subduction zone in the figure.
D
According to the data on this map, what kind of boundary is found between the Americas and Africa?
divergent
An expedition brings up a piece of rock from the Gauss normal epoch. According to the figure, what is the probability that it came from a time when the magnetic field is the same as today?
very likely
