Earth Shamans (大地の祈祷師, Daichi no kitō-shi) are special individuals in which have a unique connection to nature and the Earth itself.
An Earth Shaman maintains a special connection to nature and the Earth itself, able to sense and "hear" nature, such as pollution. Medusa Gorgon compares the "cries of nature" that an Earth Shaman can hear at times to the equivalent of a child to their parents. Earth Shamans also have other unique abilities. Due to the connection of the Earth, they're especially able to communicate with the Earth and can even find secret passages to underground locations.
It seems that an Earth Shaman also has hidden abilities in which can only be awakened whenever Magic is directed into the Earth Shaman themselves. When used on Fire and Thunder, this resulted in them aging from small children to resemble the ages of a teenager as well as augment their powers.