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Summary of Continental Drift and Seafloor Spreading
1. Continental Drift
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The Big Idea: Millions of years ago, all the continents were joined together in one giant supercontinent called
Pangaea. Over time, they drifted apart to their current positions.
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Who proposed it? A scientist named
Alfred Wegener.
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Evidence for Drift:
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Fit of Continents: The coastlines of South America and Africa look like puzzle pieces that fit together.
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Rock & Mountain Similarities: Mountain ranges and rock types on different continents match up (e.g., mountains in North America match those in Europe).
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Fossil Evidence: Fossils of the same plants and animals (like the reptile *Mesosaurus*) are found on continents now separated by oceans.
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Past Climates: Rocks show evidence of past climates that don't match the current location (e.g., tropical plant fossils found in cold areas today), suggesting those lands used to be closer to the equator.
2. Seafloor Spreading
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How it works: This process explains *how* the continents move. It happens at
mid-ocean ridges (underwater mountain ranges).
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The Process:
1. Hot magma rises from Earth’s mantle.
2. It pushes up through the crust at the ridge.
3. New ocean crust forms as the magma cools.
4. Older crust is pushed away from the ridge on both sides.
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Result: The ocean floor gets wider, pushing the continents attached to it further apart.
3. Modern Proof
* Today, scientists use
satellites and GPS to track the movement of tectonic plates. They can measure exactly how fast continents are moving apart (a few centimeters per year).
Final Answer:
The text explains that
Continental Drift is the theory that continents were once joined in a supercontinent called Pangaea and have moved apart over millions of years. Evidence includes matching fossils, rock formations, and coastline shapes across different continents.
Seafloor Spreading is the mechanism that drives this movement: new ocean crust is created at mid-ocean ridges as magma rises and cools, pushing older crust and the continents aside. Modern technology like GPS confirms these plates are still moving today.
Parent Tip: Review the logic above to help your child master the concept of seafloor spreading worksheet.
