Plate Tectonics worksheet focusing on continental drift and seafloor spreading concepts.

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Here's the completed and explained version of the worksheet:

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Section 1: Continental Drift

A. The continental drift hypothesis—continents have moved slowly to their current locations.

1. All continents were once connected as one large landmass now called
➤ Pangaea
*(Explanation: Alfred Wegener proposed that all continents were once joined in a supercontinent he named Pangaea, which later broke apart and drifted to their current positions.)*

2. The main body parts and the shape defined by the present positions.
➤ Shape
*(Explanation: One piece of evidence for continental drift is the way the edges of continents (like South America and Africa) fit together like puzzle pieces.)*

3. Evidence for continental drift:
a. Fossils of the same organisms found on different continents.
*(Explanation: Identical fossils of plants and animals found on continents now separated by oceans suggest they were once connected.)*

b. Similar rock layers have been found on different continents.
*(Explanation: Matching geological formations across continents support the idea that they were once joined.)*

c. Remains of warm-weather plants in cold regions and glacial deposits in warm regions.
*(Explanation: This suggests continents have moved from one climate zone to another over time.)*

4. At first, continental drift was not accepted because no one could explain how or why continents had moved.
*(Explanation: Wegener couldn’t provide a convincing mechanism for how continents moved through the ocean floor, which led scientists to reject his theory initially.)*

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Section 2: Seafloor Spreading

A. Using sonar (sound navigation ranging), scientists discovered a system of underwater mountain ranges called the mid-ocean ridges in many oceans.
*(Explanation: Sonar technology allowed scientists to map the ocean floor and discover the mid-ocean ridge system, a key feature of seafloor spreading.)*

B. In the 1960s, Harry Hess suggested the theory of seafloor spreading to explain the ridges.

1. Melted rock material (magma) rises up from the mantle at the mid-ocean ridges.
➤ Magma rises upward to the surface at the mid-ocean ridges.
*(Explanation: As tectonic plates pull apart at divergent boundaries, magma rises from the mantle to fill the gap, forming new oceanic crust.)*

2. Then, it flows sideways, carrying the newly formed oceanic crust away from the ridge.
*(Explanation: The newly formed crust moves outward from the ridge as more magma rises behind it.)*

3. As the seafloor spreads apart, magma moves up and flows from the cracks, cools, and forms new seafloor.
*(Explanation: This continuous process creates new oceanic crust and pushes older crust away from the ridge.)*

C. Evidence for seafloor spreading:

1. Magnetic rocks are located at mid-ocean ridges.
*(Explanation: As lava cools, iron-rich minerals align with Earth’s magnetic field. Reversals in Earth’s magnetic field are recorded in these rocks, creating symmetrical patterns on either side of the ridge.)*

2. Several of Earth’s magnetic field are recorded by rocks in strips parallel to ridges.
*(Explanation: These alternating magnetic stripes provide strong evidence that the seafloor has spread symmetrically from the mid-ocean ridge.)*

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✔ Summary of Key Concepts:

- Continental Drift: Proposed by Alfred Wegener; continents were once joined in Pangaea and have moved.
- Evidence: Fossils, rock layers, climate indicators.
- Seafloor Spreading: Proposed by Harry Hess; new oceanic crust forms at mid-ocean ridges and spreads outward.
- Evidence: Magnetic striping, age of oceanic crust, sonar mapping.

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