COS 7: Plate boundaries

old crust is recycled by subduction

At an oceanic-oceanic convergent boundary, ____.

matching coastlines

Many early mapmakers thought Earth's continents had moved based on ____.

20 km away from the Mid-Atlantic Ridge

Base your answer to the question on the cross section below and on your knowledge of Earth science. The cross section represents the distance and age of ocean-floor bedrock found on both sides of the Mid-Atlantic Ridge. {timeline picture} According to the cross section, every 1 million years, the ocean floor bedrock moves approximately ____

younger

Compared to ocean crust near deep-sea trenches, crust near ocean ridges is ____.

Wegener couldn't explain why or how the continents moved

Continental drift was not widely accepted when it was first proposed because ____.

very tall mountain ranges

Continental-continental plate collisions produce ____.

from warmer regions to cooler regions

Convection currents transfer thermal energy ____.

transform boundary

Crust is neither destroyed nor formed along which of the following boundaries?

arrows pointing towards each other

Draw a diagram that depicts what happens at convergent boundaries.

arrows pointing away from each other

Draw a diagram that depicts what happens at divergent boundaries.

arrows sliding past each other (opposite directions)

Draw a diagram that depicts what happens at transformational boundaries.

one convection current rotating clockwise and the other matching convection current counterclockwise

Draw a diagram which correctly shows how mantle convection currents are most likely moving beneath colliding lithospheric plates.

youngest near ocean ridges

Isochron maps of the seafloor indicate that ocean crust is ____.

2,3,4,1,5

Put convection process in chronological order: 1=Gravity pulls cooler matter downward. 2=Matter is heated. 3=The matter expands and decreases in density. 4=Warmed matter is forced upward. 5=An up-and-down flow of matter produces a convection current.

5,1,3,2,4

Put seafloor spreading in chronological order: 1=Crust spreads along an ocean ridge and magma fills the gap that is created. 2=New ocean floor forms as the magma hardens. 3=New seafloor moves away from the ridge, cools, and becomes more dense than the material beneath it. 4=The seafloor contracts and sinks. 5=Hot magma which is less dense than surrounding material, is forced toward the crust.

igneous rock with normal magnetic polarity

Use the graphic below to answer questions below [picture of crust layer with rock symbols] If the crust symbol represents basalt with normal magnetic polarity, what does the crust symbol most likely represent?

the reverse of today

According to the data shown in the figure, what was Earth's magnetic polarity like 5 million years ago?

very likely

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?

new ocean crust

Each cycle of spreading and intrusion of magma during seafloor spreading results in ____.

ocean ridges

Features found at divergent boundaries include ____.

Fold mountains are mountains that form mainly by the effects of folding on layers within the upper part of the Earth's crust. Before either plate tectonic theory developed, or the internal architecture of thrust belts became well understood, the term was used for most mountain belts, such as the Himalayas.

Know location of highly-folded mountains in picture.

A rift valley is a linear-shaped lowland between several highlands or mountain ranges created by the action of a geologic rift or fault

Know location of rift valley in picture.

subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate and sinks into the mantle as the plates converge.

Know location of subduction zone on a picture.

It consists of various volcanically active mountains linked in chains, typically having a valley known as a rift running along its spine.

Know location of volcanic ridge in picture.

a deep-sea trench

Subduction results in the formation of ____.

pulls tectonic plates toward one another

The downward part of a convection current causes a sinking force that ____.

mantle

The driving forces of tectonic plates are related to convection currents in Earth's ____.

a temperate, rainy climate

The existence of coal beds in Antarctica indicates that the continent once had ____.

a mirror image of that of the other side

The magnetic pattern of ocean-floor rocks on one side of an ocean ridge is ____.

near ocean ridges

The youngest part of the ocean floor is found ____.

rising convection currents in the magma

Use the graphic below to answer questions below [picture of ocean floor] The geologic features on the ocean floor in this region resulted from _____________.

a reversal of todays magnetic field

What is the magnetic field for the Gauss normal epoch?

either normal or reversed magnetic polarity (based on what the Earths polarity is at the time of formation)

What type of polarity does basalt have?

igneous rock (made in volcanos) that takes the magnetic field of the earth in the time it was created

What type of rock is basalt?

it show a reversal of todays magnetic field

What was Earth's magnetic polarity like 5 million years ago?

Molten rock is less dense than the cooler, solid rock around it

Why does molten rock in Earth's mantle rise to Earth's lithosphere in a convection current?

Glossopteris

____ is a fossil fern that helped support Wegener's hypothesis of continental drift.