Counter current involves blood in the capillaries flowing in the opposite direction to the flow of water flowing over them. Gases diffuse faster from one area to another when the concentration difference between the two areas is at its greatest, as compared to when the concentration difference is low.
Older oceanic crust, which is more dense than continental crust, has long since been recycled in the process of subduction. Credit: U.S. Geological Survey. Plate tectonics shapes the surface of our planet, but it also runs much deeper: Plate movement is the surface expression of convection in Earth's interior.
