In the Last Airbender epsiode "The Cave of Two Lovers", it tells the story of the first Earthbenders (Oma and Shu). Each lived on two towns that were warring with each other. They meet in secret in a mountain and, after learning Earth bending from the Badgermoles, constructed those tunnels.



In book 2 of Korra, it claims bending was given by the Lionturtles when everyone use to live on lionturtles. How can they have bending at the beginning when Oma and Shu (back at some time after humans started living off of lionturtles) be the FIRST Earthbenders?



As far as learning martial arts with waterbending, I think that is something either:

1--Attempting to mimic water/ocean movements/waves.

2--something developed overtime by early waterbenders to improve on their bending and combat style.



Another contradiction is the whole "spirits being kept from the physical world" and those portals they introduced. The whole aspect of the spirit world (to me at least) by definition is a non-physical world and only spirits can dwell (meaning impossible for physical bodied humans to enter). Plus the spirits were shown (in Last Airbender series) to travel back and forth from spirit world and physical world. The "Painted Lady" was another spirit that entered the physical world, granted it was to thank Katara for her help but you see my point. Remember than panda-like spirit Heibei? He went to the human world, kidnapped humans (even Sokka), and took them to the spirit world as prisoners. In book 2 of Korra, it was claimed that the spirits were KEPT from entering the physical world once the portals were closed.





In my personal opinion of the origin of the avatar, the "avatar" wasn't originally a human but the top good spirit that took half-human form that could bend all the elements. This, again in my thinking, was to try and restore balance when its dark counterpart/devil screwed up 'paradise'. To me, it would have been better to introduce this concept (Raava being the top spirit and first avatar, which Korra is the reborn version of). The whole thing of Amon leanring his skill from the spirits, (in my own personal story idea) what if it really did come from a spirit... a dark spirit that (if the half human half spirit avatar was finally gone for good) it/she would rule the world!