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Understanding Earth
chapter 2
18
Geology
Not Applicable
09/24/2005

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Term
Tectonics (tekton meaning builder)
Definition
The general term used by early geologists to describe mountain building, volcanoes, and other processes that construct geologic features on Earth's surface
Term
Continental Drift
Definition
Large-scale movements of continents over the globe
Term
Gondwanaland (or Gondwana)
Definition
Eduard Suess' theory that the combined present-day southern continents had onced formed a single giant continent called this
Term
Panagaea
Definition
Greek for "all lands," it was the supercontinent proposed by Alfred Wegener
Term
Seafloor Spreading
Definition
Convection in Earth's mantle can push and pull the continents apart, creating new oceanic crust through this process
Term
Divergent Boundaries
Definition
Plates move apart and new lithosphere is created
Term
Convergent Boundaries
Definition
Plates come together and one is recycled back into the mantle (plate area decreases)
Term
Transform-fault boundaries
Definition
Plates slide horizontally past each other (plate area remains constant)
Term
Spreading Centers
Definition
Mid-ocean ridges
Term
Oceanic Plate Separation
Definition
An example is the Mid-Atlantic Ridge
Term
Continental Plate Separation
Definition
Examples are the East African Rift and the Rhine Valley
Term
Subduction
Definition
The act of one oceanic plate descending beneath the other in an ocean-ocean convergence
Term
Island Arc
Definition
The cold lithospheric slab descends, the pressure increases, and the water trapped in the rocks of subducted oceanic crust is squeezed out. It rises into the asthenosphere above the slab. This fluid causes the mantle to melt, producing a chain of volcanoes, called this, on the seafloor beneath the trench.
Term
Transform Faults
Definition
Fractures along which relative displacement occurs as horizontal slip between the adjacent blocks (San Andreas Fault is a prime example, the Pacific Plate slides by the North American Plate)
Term
Magnetic Anomalies
Definition
Long, narrow bands that are parallel and almost perfectly symmetrical with respect to the crest of the mid-ocean ridge. The magnetic field alternates between high and low values in these.
Term
Magnetic Time Scale
Definition
(1) Earth's magnetic field reverses its diection in intervals of tens of thousands of years and (2) seafloor spreading gradually moves newly magnetized crust away from the ridge crest
Term
Relative Plate Velocity
Definition
The velocity at which one plate moves relative to the other plate
Term
Isochrons
Definition
Contours that connect rocks of equal age
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