What are convection currents and what causes them?

convection currents occur when a heated fluid expands, becoming less dense, and rises. The fluid then cools and contracts, becoming more dense, and sinks.
Convection currents are an important form of heat transfer. Convection occurs when heat cannot efficiently be transferred through radiation or thermal conduction. In astronomy convection currents occur in the mantle of , and presumably some other planets, and the convection zone of .
Inside of the Earth, magma is heated near the core, rises toward the crust, then cools and sinks back toward the core. It is thought that this motion is responsible for the movement of the Earth’s crust.
In the sun, convection occurs when opaque gas absorbs energy emitted by fusion, heats up, and rises to the photosphere, where the energy is radiated into space. You can see convection cells in pictures of the Sun’s surface.
Convection also occurs in a pot of boiling water, or a convection oven