The historical Buddha often is pictured touching the earth with his right hand. This pose recalls his enlightenment.
As the about-to-be Buddha, Siddhartha Gautama, sat in meditation, the demon Mara claimed that the seat of enlightenment rightfully belonged to him and not to the mortal Siddhartha. Mara's army of demon soldiers cried out together, "I am his witness!" Mara challenged Siddhartha, "Who will speak for you?"
Then Siddhartha reached out his right hand to touch the earth, and the earth itself spoke: "I bear you witness!" Mara disappeared. And as the morning star rose in the sky, Siddhartha Gautama realized enlightenment and became a Buddha.