Page 161 - Science Course 2 (Book 2)

Mo11-L5b: Evidence Supporting Seaf oor Spreading

reversed polarity Sometimes a magnetic reversal occurs and the
magnetic f eld reverses direction.
when magnetized objects reverse direction and ori-
ent themselves to point south.
N N

S S

The opposite of normal polarity is reversed polarity:
a state in which magnetized objects reverse
direction and orient themselves to point south.

Let’s Begin

Development of a Theory

The f rst evidence used to support seaf oor
spreading was discovered in rocks on the seaf oor.

Scientists studied the magnetic signature of
minerals in these rocks.

N

Earth’s magnetic f eld today is described as having
normal polarity—a state in which magnetized ob- S
jects, such as compass needles, will orient them-
selves to point north.

Reversed magnetic f eld

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