5. Worldwide, the oldest rocks at the ocean floor are about 180 million years old. In contrast, the oldest continental rocks are approximately 4 billion years old.Is this observation consistent with the observed tendency for oceanic rather than continental lithosphere to descend into the mantle beneath ocean trenches?Is it consistent with the observed density of oceanic (3.0 g/cm3) versus continental (2.8 g/cm3) crust?

Continental crust is very much older than oceanic crust. Because continental crust is very rarely destroyed and recycled in subduction processes.Many rocks on continental crust are nearly as old as the earth itself.The ocean floor acts similar to conveyor belt in which oceanic crust moves away from the ocean ridge axis as more magma rises from below forming new oceanic crust.The solidified oceanic crust moves laterally away from the oceanic ridge. The seafloor is younger on either side of mid ocean ridge and becomes older at distance farther from ridge. It finally subducts under continental lithospheric plate due to density difference. The continental crust has density of 2.8 g/cm3 and the oceanic crust has density of 3.0 g/cm3. Thus, comparatively higher density oceanic crust subduct into comparatively low density continental crust at convergent plate boundaries as according to plate tectonics theory. Due to subduction, older oceanic crust disappear and melted down in asthenosphere. Thus, the oldest continental rocks are approximately 4 billion years old but the oldest rocks at the oceanic crust floor are about 180 million years old.

Answered: Worldwide, the oldest rocks at the…

Applications and Investigations in Earth Science (9th Edition)

9th Edition

ISBN:9780134746241

Author:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa

Publisher:Edward J. Tarbuck, Frederick K. Lutgens, Dennis G. Tasa

Chapter1: The Study Of Minerals

Section: Chapter Questions

Problem 1LR

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5. Worldwide, the oldest rocks at the ocean floor are about 180 million years old. In contrast, the oldest continental rocks are approximately 4 billion years old.

Is this observation consistent with the observed tendency for oceanic rather than continental lithosphere to descend into the mantle beneath ocean trenches?
Is it consistent with the observed density of oceanic (3.0 g/cm³) versus continental (2.8 g/cm³) crust?

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