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30 Cards in this Set

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  • Back

Continental drift hypothesis

continents have moved slowly to their current locations


all continents were once connected as one large landmass now called _______


similar ________ have been found on different continents

warm-weather plants

have been found in arctic areas

glacial deposits

have been found in tropical areas

mid-ocean ridges

a system of underwater mountain ranges

Harry Hess

suggested the theory of seafloor spreading to explain the ridges in the 1960s

seafloor spreading

1. Hot, less dense material below Earth's crust rises upward to the surface at the mid-ocean ridges

2. then, it flows sideways, carrying the seafloor away from the ridge

3. As the seafloor spreads apart, magma moves up and flows from the cracks, cools and forms new seafloor


rocks are located at mid-ocean ridges

reversals of Earth's magnetic field

are recorded by rocks in strips parallel to ridges

continental crust

made of granite; 20-30 miles thin (30-50 km)

oceanic crust

basalt; 3-4 miles thin (5-7 km)

upper mantle

cool, brittle

lower mantle

warm, soft

geothermal gradient

gradually gets warmer


2000 miles (3000 km) thick; is composed of the upper and lower mantle


2000 miles (3000 km) thick; is composed of the inner and outer core

inner core


outer core



Earth's crust and part of the upper mantle are broken into sections


100 km thick and is less dense than the material underneath; made of the crust and part of the upper mantle


plastic like layer below the lithosphere

divergent boundary

the boundary between two plates that are moving apart

rift valley

a place where a valley has formed where a continental plate is being pulled apart

convergent boundary

the boundary between two plates that are moving together

subduction zone

the area where an oceanic plate goes down into the mantle

transform boundary

occurs where two plates slide past one another; site of many earthquakes

convection current

cycle of heating, rising, cooling, and sinking

strike-slip fault

rocks on opposite sides of the faults move in different directions

1-12 cm

On average, the rate of movement per year