Science Chapter 17

Seafloor Spreading

Henry Hess's theory that new ocean crust is formed in mid-ocean ridges and destroyed at deep-sea trenches; occurs in a continuous cycle of magma intrusion and spreading

Subduction

process by which one tectonic plate slips beneath another tectonic plate

Transform boundary

A place where two plates slide laterally past each other is called a _________.

Pangaea

Ancient landmass made up of all the continents that began to break apart about 200 million years ago

Magnetic Reversal

Changes in Earth's magnetic field over geologic time, recorded in ocean-floor rocks and continental basalt flows.

Magnetometer

Device used to map the ocean floor that detects small changes in magnetic fields

Rift Valley

Long, narrow depression that forms when continental crust begins to separate at a divergent boundary

Convergent boundary

Place where two of Earth's tectonic plates are moving apart; associated with volcanism, earthquakes, and high heat flow; found primarily on the seafloor

Direct boundary

Place where two of Earth's tectonic plates are moving toward each other; associated with trenches island arcs, and folded mountains

Transform Boundary

Place where two tectonic plates slide horizontally past each other that is characterized by long faults and shallow earthquakes

Theory of plate tectonics

States that Earth's crust and upper mantle are broken into plates, which are huge rock slabs that move in different directions at different rates over Earth's surface.

Paleomagnetism

Study of Earth's magnetic record using data gathered from iron-bearing minerals in rocks that have recorded the orientation of Earth's magnetic field at the time of their fromation.

Less than

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.

Plowing through oceanic crust

Wegener proposed that the continents were __________________.

Continental Drift

Wegener's hypothesis that the continents were joined as a single landmass, called pangaea, that broke apart about 200 million years ago and slowly moved to their present positions.

Rising molten magma

What causes the seafloor to spread?

Ridge push

Tectonic process associated with convection currents in Earth's mantle that occurs when the weight of an elevated ridge pushes an oceanic plate toward a subduction zone

slab push and ridge pull

How are the convection currents set in motion?

Slab pull

Tectonic process associated with convection currents in Earth's mantle that occurs as the weight of the subducting plate pulls the trailing lithosphere into the subduction zone

Fossil data

What evidence did Wegener use to estimate the time of Pangaea's break up?

a line on a seafloor map that connects points of the same age

What is an isochron?

Continental Drift

What is the name of Alfred Wegener's hypothesis about moving landmasses?

Subduction

What is the process called when one plate is forced beneath another at a convergent plate boundary?

Paleomagnetism

What is the study of Earth's magnetic record?

Convection currents in the mantle

What is thought to be the driving mechanism of plate movement?

Mid-ocean ridges and deep sea trenches

What two topographic features of the ocean floor were discovered only with the use of sonar?

Seafloor magnetic data

Which type of information was NOT collected by Wegener to support his continental drift hypothesis?

Existence of coal beds

Why did Wegner think that the Antarctic continent had been closer to the equator in the geologic past?