[quote=Hank]
Waterbenders can turn water into ice or heat it up into steam. There's no reason earthbenders shouldn't be able to do the same to their respective element. The fundamental mechanics behind it are , because that's what it is.
[/quote]

I think it makes sense because the atoms of each controlled element can be excited with friction to change form.

Inb4 the writers make a plasma bender out of the air benders.