Evidence of Polar Reversals
Worksheet
1. What geological process forms magnetic stripes on the seafloor?
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A) Tectonic plate collisions
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B) Seafloor spreading
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C) Subduction zones
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D) Volcanic eruptions
2. What aligns with Earth's magnetic field during the formation of new oceanic crust?
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A) Seawater
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B) Iron-rich minerals in magma
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C) Sedimentary rocks
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D) Organic matter
3. What phenomenon is recorded by the alternating pattern of magnetic stripes on the seafloor?
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A) Seafloor erosion
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B) Polar ice melting
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C) Earthquakes
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D) Polar reversals
4. How do scientists determine the age of oceanic crust and correlate it with known periods of polar
reversals?
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A) By measuring the temperature of the ocean water
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B) By studying the density of the ocean floor
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C) By analyzing the composition of marine life
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D) By measuring the ages of oceanic crust on either side of mid-ocean ridges
Fill in the Blank:
1. The process that forms magnetic stripes on the seafloor is called _________.
2. Iron-rich minerals in ________ align with Earth's magnetic field during the formation of new oceanic crust.
3. The alternating pattern of magnetic stripes on the seafloor indicates periods of normal and reversed
_________.
4. By measuring the ages of oceanic crust on either side of mid-ocean ridges, scientists can correlate the
magnetic stripe patterns with known periods of _________ reversals.
Evidence of Polar Reversals
Evidence of Polar Reversals: Over geological time scales, the Earth's magnetic field has undergone reversals,
where the magnetic north and south poles switch places.
The stripes on the seafloor are related to Earth's magnetic field through a process called seafloor spreading.
Here's how they're connected:
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Seafloor Spreading:
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Occurs at mid-ocean ridges, where new oceanic crust is formed as magma rises from below the
Earth's surface.
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As magma cools and solidifies, it becomes oceanic crust.
Alignment with Magnetic Field:
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Iron-rich minerals in the cooling magma align themselves with Earth's magnetic field like tiny
compass needles.
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When the minerals solidify into rock, they "freeze" the direction of the magnetic field at that time.
Formation of Stripes:
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As more magma wells up and spreads outward at the ridge, new rock with aligned magnetic
minerals is continually added to the ocean floor.
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Over time, as the Earth's magnetic field periodically flips its polarity, the newly formed rocks
preserve these magnetic changes.
Alternating Stripes:
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This results in a pattern of alternating magnetic stripes on the seafloor, reflecting the history of
magnetic field reversals.
Study and Interpretation: By studying these magnetic stripes, scientists can decipher the history of
Earth's magnetic field reversals and understand the process of seafloor spreading.