To solve the problem and explain the solution, let's break down the worksheet step by step:
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Section 1: Mid-Ocean Ridges
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A. Definition of Mid-Ocean Ridge
- A mid-ocean ridge is an underwater mountain chain where new oceanic crust is formed due to volcanic activity. This process occurs as tectonic plates move apart, allowing magma to rise from the mantle and solidify into new crust.
Answer:
New oceanic crust
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B. Discovery of Mid-Ocean Ridges
- Scientists discovered mid-ocean ridges using sonar. Sonar (Sound Navigation and Ranging) is a technique that uses sound waves to locate objects underwater by recording the echoes of these sound waves.
Answer:
Sonar
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Section 2: Sea-Floor Spreading
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A. Alfred Wegener and Harry Hess
- Alfred Wegener was a German meteorologist and geophysicist who proposed the theory of continental drift in the early 20th century. His idea suggested that continents were once joined together in a supercontinent called Pangaea and have since drifted apart.
- Harry Hess, an American geologist, studied mid-ocean ridges and provided evidence that supported Wegener's idea of continental drift. Hess proposed that sea-floor spreading occurs at mid-ocean ridges, where new crust forms as tectonic plates move apart.
Answer:
Harry Hess
Continental Drift
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B. Evidence for Sea-Floor Spreading
- The concept of sea-floor spreading is supported by several lines of evidence:
1.
Magnetic Stripes on the Ocean Floor: As new crust forms at mid-ocean ridges, it cools and records the Earth's magnetic field at the time of its formation. Over millions of years, the Earth's magnetic field reverses, leaving a pattern of alternating magnetic stripes symmetrically on either side of the mid-ocean ridge.
2.
Age of Oceanic Crust: Rocks near the mid-ocean ridge are younger, while those farther away are older. This indicates that new crust is continuously forming at the ridge and moving outward as the plates spread.
3.
Volcanic Activity: Volcanoes and earthquakes are common along mid-ocean ridges, indicating active plate movement and magma upwelling.
4.
Symmetry of Features: The topography and features on either side of the mid-ocean ridge are symmetrical, suggesting that the two sides are moving away from each other.
Answer:
Evidence for Sea-Floor Spreading includes:
1. Magnetic stripes on the ocean floor
2. Age of oceanic crust
3. Volcanic activity
4. Symmetry of features
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Final Answer
1.
Mid-Ocean Ridges
- A. New oceanic crust
- B. Sonar
2.
Sea-Floor Spreading
- A. Harry Hess; Continental Drift
- B. Evidence for Sea-Floor Spreading:
- Magnetic stripes on the ocean floor
- Age of oceanic crust
- Volcanic activity
- Symmetry of features
Boxed Final Answer:
\[
\boxed{
\text{New oceanic crust, Sonar, Harry Hess, Continental Drift, Magnetic stripes on the ocean floor, Age of oceanic crust, Volcanic activity, Symmetry of features}
}
\]
Parent Tip: Review the logic above to help your child master the concept of seafloor spreading worksheet.
