Earth Dynamics – Modern plate tectonics Which statement(s) correctly describe the modern theory of plate tectonics and seafloor dynamics?
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Athe creation of oceanic crust and the drifting of continents
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Bthe convention currents within the earth's mantle cause the creation of new oceanic crust at the mid oceanic ridges
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Cthat the oceanic crust is destroyed at areas where this crust type becomes subducted under the lighter continental crust
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DAll of the above
Answer
Correct Answer: All of the above
Explanation
Introduction / Context:Plate tectonics integrates continental drift and seafloor spreading into a single framework. Lithospheric plates move over the asthenosphere, creating, transporting, and recycling oceanic crust while reshaping continents and ocean basins.
Given Data / Assumptions:
- (a) addresses seafloor creation and continental motion.
- (b) attributes ridge volcanism/spreading to convective circulation within the mantle (spelled “convection”).
- (c) describes subduction zones where dense oceanic plates descend beneath lighter continental (or oceanic) plates.
Concept / Approach:All three statements are essential elements of plate tectonics: seafloor spreading at mid-ocean ridges, plate motion driven in part by mantle convection (plus slab pull and ridge push), and destruction/recycling of oceanic crust at subduction zones. Hence the comprehensive answer includes all.
Step-by-Step Solution:Confirm creation: new basaltic crust forms at ridges.Confirm motion: continents ride on plates that drift relative to one another.Confirm destruction: old oceanic crust is consumed at trenches via subduction.Therefore choose “All of the above”.
Verification / Alternative check:Age of oceanic crust increases away from ridges and is youngest at ridge axes; deep earthquakes and trenches mark subduction—observations consistent with all statements.
Why Other Options Are Wrong:Each single statement is correct but incomplete. The theory requires the full cycle: creation, motion, and destruction.
Common Pitfalls:Focusing only on continental drift and forgetting seafloor recycling; or thinking continents plow through oceanic crust without plate interactions.
Final Answer:All of the above