The earth has a magnetic north and south. How does this help up with evidence to support the theory of Continental Drift?
The first key piece of evidence for plate tectonics was the paper by Fred Vine and Drum Matthews showing that the ocean floor had magnetic stripes that are symmetric about the ocean ridge. Basaltic magma is erupted at the ridge and the magnetite in it lines up with the Earth's magnetic field. The plates move apart and more material is erupted and intruded and adopts the magnetic field. Every now and then (the last time was 0.78 million years ago) the Earth's magnetic field reverses. When this happens the next batch of magma adopts an orientation the reverse of the previous one. This occurs many times over millions of years. Thus, going away from the ridge, one passes over "normal" and "reversed" polarity sections of the crust and they are mirror images on each side of the ridge. Once that was published, the majority of geological opinion changed to a positive view of plate tectonics
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The Earth's magnetic field and its alignment with the continents provide evidence to support the theory of Continental Drift. Here's how this works:
1. Polar wandering: Over the course of Earth's history, the positions of the magnetic north and south poles have changed. This phenomenon is known as polar wandering. By examining the orientation of ancient rocks and minerals, geologists can determine the past positions of the magnetic poles.
2. Paleomagnetism: Rocks contain tiny magnetic minerals, such as magnetite, that align themselves with the Earth's magnetic field during their formation. These minerals effectively record the direction and strength of the magnetic field at the time the rock was formed.
3. Magnetic anomalies: When the seafloor spreads at mid-ocean ridges, magma rises from the Earth's mantle, cools, and solidifies into new rock. As the rock forms, the magnetic minerals within it align with the Earth's magnetic field at that time. Since the Earth's magnetic field periodically switches direction (known as magnetic reversals), these rocks preserve a record of these reversals.
4. Seafloor spreading: As new oceanic crust forms at mid-ocean ridges and spreads apart, it carries with it a magnetized record of the Earth's magnetic field at the time of its formation. This creates a "striped" pattern of magnetic anomalies on either side of the ridge.
5. Matching magnetic patterns: When researchers discovered these magnetic anomalies preserved on the seafloor, they noticed that the patterns of magnetic reversals on one side of a mid-ocean ridge matched those on the other side. This observation led to the development of the theory of seafloor spreading, a significant aspect of the larger theory of Continental Drift.
6. Fit of continent puzzle pieces: By analyzing the seafloor magnetic patterns and the continents' positions, scientists realized that the magnetic "stripes" on one side of the mid-ocean ridges matched remarkably well with the coastlines of continents on the other side, suggesting that they were once joined together.
In conclusion, the Earth's magnetic field played a crucial role in supporting the theory of Continental Drift by providing evidence through polar wandering, paleomagnetism, magnetic anomalies, and the fit of the seafloor patterns with the continents.