Convection Currents are a type of heat transfer created when the density of the molecules in a liquid layer of the earth change due to temperature.

Convection Currents are known as one of the three types of heat transfers. They occur in liquids, which is why certain layers of the earth such as the outer core will experience Convection Currents.

As you know, the core of the earth is much hotter than the surface. When liquid closer to the core heats up, the molecules will spread out. This will cause the material to be less dense than the surrounding material. So, the less dense material will rise closer to the layer above. As it cools closer from the surface, the molecules will press together again, become more dense, and sink. This creates a continual cycle known as convection currents.

Visit this site for more information and useful examples. Hope this helps;) http://study.com/academy/lesson/what-are-convection-currents-definition-examples-quiz.html