Magnetic Reversals and Rock Dating

by
Kevin Oliver
College Student

Magnetic striping is a concept developed by scientists studying the ocean floor. Along the ocean floor, scientists have noticed an interesting pattern. Magnetic minerals in rocks that lie near ocean ridges have reversed polarities. The figures below illustrate patterns in rocks that have formed. Some of the rocks in one strip have a normal polarity, so that a compass would register north correctly. Some of the rocks in alternating strips, however, have a reversed polarity, so that a compass would register "north" as being "south" incorrectly. Scientists have asked the question, "How does the magnetic striping pattern form?"

Scientists studied the rocks on the ocean floor for many years, and came up with the following information: " (1) at or near the crest of the ridge, the rocks are very young, and they become progressively older away from the ridge crest; (2) the youngest rocks at the ridge crest always have present-day (normal) polarity; and (3) stripes of rock parallel to the ridge crest alternated in magnetic polarity (normal-reversed-normal, etc.), suggesting that the Earth's magnetic field has flip-flopped many times" (Kious & Tilling, 1996).

Think about this evidence. What is happening along the ocean ridges? Scientists do not know why the earth's magnetic field has flip-flopped so many times. But, from the different patterns and ages in the rocks, we can determine what is happening here. What do you think is happening? How is it affecting the earth's surface? Record your thoughts as an evidence note in Mildred.