Chapter 2 Geology
Continental drift
Large-scale movements of continents across earth's surface, driven by the plate tectonic system.
What is a true statement about the ages of the continental and oceanic crust?
Most of the continental crust is older than the oceanic crust.
How are scientists able to learn information about the earth's geologic past from mid-ocean ridge volcanoes?
The iron in the layers records the direction of the earth's magnetic field, whereas the depth and location of the layer determines age.
What does NOT happen as the seafloor spreads?
The magma inside the earth becomes magnetized as it upwells to the spreading ridge.
seafloor spreading
The mechanism by which new ocean crust is formed at a spreading center on the crest of a mid-ocean ridge. As two plates move apart, magma wells up into the rift between them to form new crust, which spreads laterally away from the rift and is replace continually by newer crust.
The theory of plate tectonics states that because earth's surface is covered by tectonic plates, new plates are being formed at divergent boundaries and what happens as a result?
The old plate is recycled at convergent boundaries.
What information about the earth can be determined from isochrons that are of the same age but found on opposite sides of a mid-ocean ridge?
The past positions of the plates and the continents.
What initially began the process of the break up of Pagaea?
The rifting of North America and Europe.
Geodesy
The science of measuring the shape of earth and locating points on it's surface.
What was not revealed after geologists successfully mapped the Atlantic sea floor?
The seafloor is in the center of plates.
Mountain belts occur along which plate boundaries?
continent - continent and continent - ocean plate boundaries
What variables do geologists use to calculate the rate of plate movement based on seafloor spreading?
distance is measured from the mid-ocean ridge axis and time equals seafloor age based on magnetic data.
Volcanoes are associated with which of the following types of plate boundaries?
divergent and convergent
Which are the three basic types of plate boundaries?
divergent, convergent, transform
Which boundaries generally increase plate area?
divergent.
Continents are embedded in which layer of earth?
lithosphere
At a hotspot, which earth layer is melted into magma by heat that later erupts to earth's surface?
mantle layer
What is the name of relatively slender cylinders of fast-rising magma that are less than 100 km across?
mantle plumes
Pangaea
"all lands" A supercontinent that coalesced in the late Paleozoic era and comprised all present continents, then began to break up in the Mesozoic era.
How old are the oldest ocean rocks?
200 million years.
Divergent boundaries
A boundary between lithospheric plates where two plates move apart and new lithosphere is created. (compare convergent boundary; transform fault) plate area increases
Convergent boundaries
A boundary between the lithospheric plates where the plates move towards each other and one plate is recycled into the mantle. (compare divergent boundary: transform fault) plate area decreases.
Island arc
A chain of volcanic islands formed on the overriding plate at a convergent boundary by a magma that rises from the mantle as water released from the subducting lithospheric slab causes fluid-induced melting.
Isochrons
A contour that connects rocks of equal age.
Mantle plume
A narrow, cylindrical jet of hot, solid material rising from deep within the mantle, thought to be responsible for intraplate volvanism.
Transform faults
A plate boundary at which the plates slide horizontally past each other are lithosphere is neither created nor destroyed. Plate area does not change
The distance between which pair of states is changing significantly over time?
Alaska-hawaii
Mid-ocean ridge
An undersea mountain chain at a divergent boundary, characterized by earthquakes, volcanism, and rifting, all caused by the tensional forced of mantle convection that are pulling the two plates apart.
Where do hotspots form at the earth's surface?
Anywhere on a plate.
Which of the following is NOT convincing evidence that south America and Africa were once joined as one continent?
Both continents today have tropical rain forests in some areas and deserts in other areas.
Scientists studying magnetic anomaly patterns of the Atlantic seafloor are able to determine which information?
Direction and rate of the Atlantic seafloor spreading.
What variables do geologists use to calculate the rate of plate movement based on seafloor spreading?
Distance is measured from the mid-ocean ridge axis and time equals seafloor age based on magnetic data.
What happens during a magnetic reversal?
Earth's magnetic field flops about 180 degrees.
What is the name of the science of measuring the earth's shape and locating points on the surface?
Geodesy
Magnetic anomalies are sensitive to changes in which earth system?
Geodynamo
A better understanding of which facets of geology do not benefit from the grand reconstruction of the continents?
Igneous rock formation from current volcanism.
What did scientists discover as they observed magnetism of seafloor rocks?
Long, narrow bands of magnetic field values that showed changes in the intensity and direction of magnetism in rocks.
What instrument do geologists use to study magnetism of rock on the seafloor?
Magnetometer
Which features are parallel and symmetrical to seafloor isochrons?
Mid-ocean ridge axes.
What happens during seafloor spreading?
Older ocean floor moves away from a mid-ocean ridge with a new seafloor forming in the resulting gap.
What happens during seafloor spreading?
Older ocean floor moves away from mid-ocean ridge with a new seafloor forming in the resulting gap.
Magnetic anomalies
One in a patter of long, narrow bands of high or low magnetic intensity on the seafloor that are parallel to and almost perfectly symmetrical with respect to the crest of a mid-ocean ridge.
What is the name of the ancient ocean that surrounded Pangea?
Panthalassa
Which organism is useful is sediment age dating?
Plankton.
What is the difference between points on the same plate compared to points on two different plates?
Points on the same plate remain fixed, whereas points on two different plates move in relation to each other.
What two forces are actually moving plates?
Pull from the weight of cold lithosphere and push from mid-ocean ridges.
What is the name of the velocity at which one plate moves respectively to another?
Relative plate velocity
Divergent boundaries form which feature?
Rift valleys
Which of the following is most likely to occur based on plate tectonics?
Rifting is opening the red sea, forming a narrow ocean basin.
What word describes a property of the earth's plates?
Rigid
What is the process by which the plates separate and oceanic crust is created?
Seafloor spreading
What forms the boundaries of all tectonic plates?
Some combination of divergent, convergent, and transform boundaries.
Which mathematical equation do geologists use to calculate the rate of plate movement based on seafloor spreading?
Speed = distance / time.
Magnetic time scale
The detailed history of earth's magnetic field reversals as determined by measuring the thermormanent magnetization of rock samples whose ages are unknown
Tectonics
The general term used to describe mountain building, volcanism, earthquakes, and other processes that construct geologic features on earth's surface.
What approximate location does the earth's magnetic north pole presently align to?
The geographic north pole
Plate tectonics
The theory that describes and explains the creation and destruction of earth's lithospheric plates and their movement over earth's surface. "builder"
Relative plate velocity
The velocity at which one lithospheric plate moves relative to another.
What is not true about magnetic anomalies?
They form after lava has cooled and rested for at least 5 million years.
What is useful about isochrons?
They tell how much time has elapsed after the rock came to the surface.
What is the name of the chain of volcanoes that forms at an ocean-ridge convergent plate boundary?
Volcanic island arc
How does a tectonic plate that is being subducted along much of its boundary tend to move compared to a tectonic plate that is not being subducted?
faster than.
What element aligns itself with the earth's magnetic field as it cools.
iron.
What was the primary reason Wegener's theory of continental drift was generally rejected by scientists?
physicist showed that his explanations for how the continents moved were inccorect.
Which theory describes the movements of plates and the forces acting on them?
plate tectonics
Which boundaries have no change in plate area?
transform