Elementals-Earth (Book One)

Eons ago, our world and the universe was created by two sisters. One made the universe and space, with all the stars, galaxies, and planets. The younger one made life on these planets, life that could sustain itself to the conditions her sister made.
Together they made an Earth, where teens were trained to be warriors with one of the four elements the younger made. They were always in teams of 4, each having the same element.
Fire.
Water.
Earth/Life.
Air/Wind.
Life so far has been peaceful. But a school that hasn't been heard from for millions of years has posed as a threat, and its up to four girls who hold different elements to stop this school from taking their peace.

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For those who used to watch Avatar, I purposely put it in the wrong order, so I wouldn't just have those comments. Feel free to post them though! ^-^