It is revealed in the pilot that Korra is able to bend both fire and earth in addition to her native element, water, at the age of four, thereby proving her status as the current Avatar to the Order of the White Lotus.
Korra is able to bend both fire and earth in addition to her native element at the age of four, thereby proving her status as the current Avatar to the Order of the White Lotus. This was what it is revealed in the pilot. Her native element is water.