Science Olympiad Dynamic Planet Practice Test

What happens as oceanic lithosphere cools and moves away from a plate boundary?

1. It becomes less dense

2. It melts back into magma

3. It sinks below continental lithosphere

4. It becomes denser and thicker

The correct answer is: It becomes denser and thicker

As oceanic lithosphere cools and moves away from a plate boundary, it undergoes a transformation that leads it to become denser and thicker. This process begins at mid-ocean ridges where the lithosphere is young and relatively hot. As it moves away from the ridge, the lithosphere gradually cools down due to the loss of heat to the surrounding ocean water. The cooling of the oceanic lithosphere increases its density. As it continues to move away from the tectonic plate boundary, the lithosphere also contracts and thickens under the weight of the overlying water and sediment. This increasing density can eventually cause the oceanic lithosphere to subduct under continental lithosphere or older, denser oceanic plates at convergent boundaries, further illustrating its increased density relative to other lithospheric materials. The process you are observing is fundamental to plate tectonics and explains various geological phenomena, such as the formation of ocean basins and the recycling of the Earth's materials within the mantle.