This piece of evidence is very compelling but requires a couple of background points:

Point 1: Lava is a mixture of melted minerals of which Iron is a very common one. Iron is attracted to the Earth’s magnetic North Pole and prefers to line up with Earth’s magnetic field. While lava is liquid, the bits of iron will tend to line up with a magnetic orientation pointing at the North Pole. When the lava solidifies, the magnetic orientation is frozen into the rock- essentially; it will have a “north end” and a “south end.”

Point 2: Back in World War II, the United States, in an effort to find any advantage that would help out submarines in the war effort, collected any type of data possible about the ocean and ocean floor. When they dragged a magnetic detector along the ocean floor, they discovered that the rocks making up the ocean bottom either had a magnetic orientation pointing to the North Pole or to the South Pole. As the magnetic detectors were dragged along the ocean floor, the orientation of the rock flipped from North to South- but never any other direction. They discovered a very quirky behavior of our planet: for some still-unexplained reason, at random times in Earth’s past, the magnetic orientation of the planet reversed- several times. In other words, if you traveled back in time with a compass, sometimes it will point north and other times it will point South.

The significance of these two points becomes clear when we have a map of the magnetic orientation of the entire Atlantic Ocean floor. Imagine that the North-oriented rocks (usually referred to as “normal polarity”) are colored white while the South-oriented (“reversed polarity”) rocks are colored black. What we will see is a striped pattern which runs parallel to the coasts of the Atlantic shores. In addition, the magnetic stripe pattern that emerges as we cross the Atlantic floor from the USA to the Mid-Atlantic Ridge is an exact mirror-image of the pattern from the Mid-Atlantic Ridge to Europe. This implies that the ocean floor is splitting at the Mid-Atlantic Ridge, new rock is being made at the ridge, and the new rock (along with its magnetic orientation) is split and each half is carried away from the ridge as the ocean floor spreads.

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