In the atmosphere, convection currents occur due to the heating of the Earth's surface by radiant energy from the sun. As the air near the ground warms, it becomes less dense and rises. Colder, dense air falls to the surface where the earth heats it, creating a cycle.
Convection currents play an important role in Earth's weather patterns. They are responsible for winds and precipitation. The warm air from the surface of the Earth carries water vapor up into the atmosphere. As the air cools, its capacity to hold water decreases, so the vapor forms clouds. In the ocean, convection heating is responsible for the ocean currents, which also affect the weather patterns.
Convection currents occur in the magma of the Earth. These currents drive plate tectonics. Radioactive decay in the core of the Earth produces enough heat to melt the rocks that form magma. The heating causes the liquid to rise toward the surface and break up the continental and oceanic crust into over 12 rigid plates. The convection currents cause the plates to spread, and the cooling magma forms new rocks. At the opposite ends of the plates, at the convergent zones, the movement pushes the edges of the plates underground where they melt and recycle to form more magma.