What are the 3 main factors that cause global convection currents to be complex on earth?

Convection currents are caused by an even temperature within something, they happen within the earth's magma, water and air. It can happen in anything that isn't solid but has parts that are cooler or warmer for instance than other parts. When something happens to be cool, it sinks and when it's hot, it'll rise.

So you know what happened and so it doesn’t repeat it’s self