Which statement describes the cyclic nature of seafloor spreading? A. Continents are created. B. New oceanic crust is created. C. Volcanoes erupt and remove crust. D. Old crust gets thicker at subduction zones.
The correct answer and explanation is:
Correct Answer: B. New oceanic crust is created.
Explanation (300 words):
Seafloor spreading is a geological process that illustrates the cyclic nature of Earth’s dynamic crust, specifically beneath the oceans. It occurs at mid-ocean ridges, which are underwater mountain ranges formed by tectonic activity. The correct statement that captures this process is “New oceanic crust is created.”
Here’s how it works: At mid-ocean ridges, tectonic plates move apart due to convection currents in the Earth’s mantle. As these plates separate, magma from the mantle rises up through the gap. When the magma reaches the surface and cools, it solidifies into new oceanic crust. Over time, this new crust is pushed away from the ridge as more magma emerges and solidifies behind it. This continuous cycle of creation, movement, and destruction of oceanic crust defines the cyclic nature of seafloor spreading.
The process does not end with the creation of new crust. As the seafloor spreads, older crust moves farther away from the ridge and eventually reaches a subduction zone—an area where one tectonic plate is forced beneath another into the mantle. In these zones, the old oceanic crust melts and is recycled into the Earth’s interior. This destruction of old crust balances the creation of new crust at mid-ocean ridges, maintaining the size of Earth’s surface and making the process cyclic.
Let’s evaluate the other options:
- A. Continents are created – Incorrect. Seafloor spreading affects oceanic crust, not continental crust formation.
- C. Volcanoes erupt and remove crust – Incorrect. Volcanoes may form at spreading ridges but do not “remove” crust in this context.
- D. Old crust gets thicker at subduction zones – Incorrect. Old crust is destroyed, not thickened, at subduction zones.
Therefore, Option B best describes the cyclic nature of seafloor spreading through the creation of new oceanic crust at mid-ocean ridges and its eventual recycling in subduction zones.