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Questions and Answers
What happens to seafloor age as you move away from mid-ocean ridges?
What happens to seafloor age as you move away from mid-ocean ridges?
Magnetic polarity is the same across the entire seafloor.
Magnetic polarity is the same across the entire seafloor.
False
What causes the movement of lithospheric plates?
What causes the movement of lithospheric plates?
Convection currents in the mantle
The new seafloor or oceanic crust is primarily composed of __________ rocks.
The new seafloor or oceanic crust is primarily composed of __________ rocks.
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Match the following processes with their descriptions:
Match the following processes with their descriptions:
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What is the primary evidence for seafloor spreading derived from molten materials?
What is the primary evidence for seafloor spreading derived from molten materials?
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Younger rocks are located farther away from the mid-ocean ridge.
Younger rocks are located farther away from the mid-ocean ridge.
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What evidence do drilling samples provide about the age of rocks on the ocean floor?
What evidence do drilling samples provide about the age of rocks on the ocean floor?
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The ocean floor rocks contain a pattern of magnetized stripes that record the reversals in the ______ field.
The ocean floor rocks contain a pattern of magnetized stripes that record the reversals in the ______ field.
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Match the type of evidence for seafloor spreading with its description:
Match the type of evidence for seafloor spreading with its description:
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What geological process occurs at divergent boundaries where tectonic plates move away from each other?
What geological process occurs at divergent boundaries where tectonic plates move away from each other?
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Seafloor spreading results in the formation of new oceanic crust.
Seafloor spreading results in the formation of new oceanic crust.
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What device is used to measure the depth of the ocean floor by sending sound waves?
What device is used to measure the depth of the ocean floor by sending sound waves?
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The normal and reversed magnetic polarity of seafloor basalts create a pattern of __________ stripes.
The normal and reversed magnetic polarity of seafloor basalts create a pattern of __________ stripes.
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Match the following features of the seafloor with their descriptions:
Match the following features of the seafloor with their descriptions:
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Which of the following is NOT a feature of the seafloor?
Which of the following is NOT a feature of the seafloor?
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Magnetometers are used to produce magnetic maps of the seafloor.
Magnetometers are used to produce magnetic maps of the seafloor.
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What evidence supports the concept of seafloor spreading?
What evidence supports the concept of seafloor spreading?
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Study Notes
Seafloor Spreading
- Seafloor spreading is a geological process where new oceanic crust forms at mid-ocean ridges, then slowly moves away from the ridges.
- This process occurs at divergent boundaries. Tectonic plates move apart, forming new seafloor.
- The movement of tectonic plates is driven by convection currents in the Earth's mantle.
- Seafloor spreading is supported by evidence from studying molten materials, magnetic stripes in the seafloor, and drilling samples from the ocean floor.
- Molten materials erupt from cracks in mid-ocean ridges, forming unique "pillow" structures.
- Magnetic stripes on the seafloor exhibit a symmetrical pattern, reflecting reversals in Earth's magnetic field.
- Older rocks are found farther from the mid-ocean ridge, while younger rocks are closer to it. This age pattern supports the idea of seafloor spreading.
- The Earth doesn't get bigger as the seafloor spreads. Subduction occurs where the older oceanic crust slides beneath the continental crust, into the mantle.
Learning Competency
- Learning Competency: Explain how seafloor spreads.
Learning Objectives
- Discuss the process of seafloor spreading.
- Explain the role of convection currents in seafloor spreading.
- Describe three pieces of evidence supporting seafloor spreading.
Echo Sounders/Sonar
- Echo sounders produce sound waves that travel outward in all directions and bounce off the nearest object, returning to the ship.
Features of the Seafloor
- Modern maps of the Atlantic and Pacific Oceans show darker blue areas corresponding to deeper seas.
- Deep sea trenches are found along the west coast of Central and South America and in the mid-Atlantic, east of the southern tip of South America.
- Isolated mountains, large mountain ranges, and stretches of flat, featureless regions are also common.
Seafloor Magnetism
- Scientists used magnetometers to discover a pattern of normal and reversed magnetic stripes in ocean floor basalts. This pattern helps date the rocks.
- The ocean floor's features include the continental shelf, continental slope, abyssal plain, mid-ocean ridge, seamounts, and trenches.
- Reversals in Earth's magnetic field are recorded in the rocks created at mid-ocean ridges.
Polar Reversals
- Earth's magnetic field sometimes reverses, alternating between periods of normal and reversed polarity.
- When the north and south magnetic poles are aligned, it's called normal polarity. When they are reversed, the magnetic field is reversed polarity.
Magnetic Stripes
- Scientists discovered a symmetric pattern of normal and reversed magnetic stripes on the seafloor. These stripes mirror the reversals in Earth's magnetic field, confirming seafloor spreading.
Seafloor Ages
- Seafloor is youngest near mid-ocean ridges, progressively older the farther one travels away from the ridge.
- Orange areas on seafloor age maps correspond to the youngest seafloor. The oldest parts of the seafloor are located near continents or deep-sea trenches.
Hess's Theory of Seafloor Spreading
- Harry Hess proposed the theory of seafloor spreading to explain continental movement.
- Hess suggested that continents do not move across oceanic crust, but that continents and ocean floor move together, with new crust formed at mid-ocean ridges through upwelling magma.
Convection Currents
- Convection currents within the Earth's mantle drive the movement of tectonic plates.
- Heat from the Earth's core causes hot mantle material to rise, cool, and sink, creating a cycle that moves the plates.
- Ridge push and slab pull contribute to plate movement.
Divergent Boundary-Fast-spreading Ridge
- Hot mantle rock rises at mid-ocean ridges.
- Melt forms beneath the lithosphere.
- Magma rises, becomes injected into the crust, and forms new crust at the mid-ocean ridge.
- Lava erupts onto the ocean floor, adding new crust.
- Plates move apart, cool, and thicken.
Processes of Seafloor Spreading
- The movement of oceanic plates at divergent boundaries causes fractures (due to tensile stress) in the lithosphere.
- Hot basaltic magma rises from the mantle and fills these fractures.
- The magma cools and solidifies, forming new seafloor.
- The new seafloor moves away from the ridge, and the cycle repeats.
- Older rocks move farther from the spreading centers than younger ones, near the spreading center.
Efficiencies that the seafloor spreads
- Evidence from molten materials (pillow rocks).
- Evidence from magnetic stripes (reversals recorded in rocks).
- Evidence from drilling samples (older rocks farther from mid-ocean ridges, youngest rocks at the ridge).
Why Doesn't the Earth Get Bigger?
- Seafloor spreading is balanced by subduction. Older oceanic crust slides beneath continental crust at subduction zones, returning to the mantle.
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Description
Explore the geological process of seafloor spreading, where new oceanic crust forms at mid-ocean ridges and moves away due to tectonic plate activity. This quiz covers the evidence supporting this process, including magnetic stripes and the formation of unique geological structures. Test your knowledge on the dynamics of Earth’s tectonics and the significance of this process in shaping our oceans.
