11. As magma rises from the mid-ocean ridge, it cools and solidifies. As this magma
solidifies, some of the minerals align with Earth's magnetic field. Every few
million years, Earth's magnetic field reverses. This reversal is recorded in the
magma that solidified after leaving the mid-ocean ridge. In the picture, these
magnetic reversals are indicated by dark and light bands.
Magnetic Orientation of Ocean Crust
volcanoes
mld-ocean ridge
volcanoes
ning
Tising
Smage
sea-floor spreading
rising magma
mantle
Courtesy of Kenneth R. Long The Cambridge Guide to the Solar System
Second Edition 2011
How con scientists tell when the reversals of the magnetic field occurredo
A. by measuring the thickness of the different bands of the oceanic crust
B. by measuring the distance between the mid-ocean ridge and the ocean
floor band
C. by measuring the amounts of minerals that aligned to Earth's magnetic
field in the different bands
D. by measuring the strength of Earth's magnetic field recorded in the
solidified magma of the oceanic crust