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Magnetic Reversals of the Seafloor


Scientists first proposed the theory of Continental Drift in 1915, and it was faced with ridicule among the scientific community. They noted that the age and composition of mountain ranges such as the Appalachian Range in the Eastern United States match up perfectly with the Caledonian Mountains of Europe. Scientists also used fossils to show that the climates of certain land masses have drastically changed from what they are today (see Figure 1). However, they were unable to prove the theory because there was little scientific evidence to prove how the continents moved. Over the years, more evidence was brought to light, and the idea of Continental Drift was strengthened to become the Theory of Plate Tectonics.

In the 1950s researchers began to study the ocean floor. They discovered the Mid-Atlantic Ridge and scientists became interested in understanding why such a large mountain range was located in the middle of the Atlantic Ocean. Over the next couple decades, further research was performed on the age and magnetic polarity of the sea floor that further validated that the continents were moving. It was discovered that the ocean floor was of different ages (see Figure 2). Also, the ocean floor has differentiating magnetic polarity moving away from the Mid-Atlantic Ridge (see Figure 3).

Watson, John M. Continental Drift Fossil Evidence. Digital image. Wikipedia. Wikimedia Foundation, 5 May 1999. Web. 15 Sept. 2016.

Figure 1

NOAA Age of Oceanic Lithosphere. Digital image. Wikipedia. Wikimedia Foundation, 8 June 2009. Web. 15 Sept. 2016.

Figure 2

United States Geological Survey. Magnetic Anomalies of the Ocean Floor. Digital image. Wikipedia. Wikimedia Foundation, n.d. Web. 15 Sept. 2016.

Figure 3

Based on Figure 3, which statement shows that Earth’s geomagnetic field provides evidence for the Theory of Plate Tectonics?


Crustal rock moving outward from the Mid-Atlantic Ridge retains a record of the Earth's magnetic field at the time when it was created.


The convergent boundary along the Mid-Atlantic Ridge destroys all evidence of magnetic polarity.


Older ocean crust eventually loses its polarity as it moves away from the Mid-Atlantic Ridge.


Newly formed ocean crust along the Mid-Atlantic Ridge has always had the same magnetic polarity.