At the Buddha's enlightenment, he pointed to the earth or touched the earth, meaning the earth (or world) was adequate witness to his spiritual accomplishment or new status, or, perhaps the only witness that would be acceptable to Mara. Mara accepted the witness. I do not understand the principle or truth of this event. Earth or the world seems to be personified in some way, or endowed with a capacity to accept or reject a plea for witnessing. Explanations and clarifications would be greatly appreciated. Thx.
PaPa, I believe touching the earth is a later addition to pali cannon, but i could be wrong. Bodhirajakumara Sutta is one of the best sutta of autobiography of Bhudda. Buddha also told Ven Anuruddha in dozens of sutta about himself from the history of sakaya clan, when he came down from Dusita into his mother's womb and so on to after the evening of enlightment.
Because it was on this earth he cultivated the ten Paramithas in 3 different ways. He was training his generals(Dana, Sila, Nekkhamma etc.) for eons for the final battle against the evil one. It wasn't a plea, he was making the ultimate statement, saying that he needs no other witness when the great earth itself has witnessed it all.
perhaps the only witness that would be acceptable to Mara
No, it wasn't a case of finding something that the Mara would accept. Mara had no way to defeat the Buddha. He had no choice but to flee in fear because the earth started trembling.
Some versions of the story include a deva named Prithvi:
Prithvi (pṛthvī, also pṛthivī) "the Vast One" is the Sanskrit name for the earth as well as the name of a devi in Hinduism and Buddhism.
In Buddhist texts and visual representations, Pṛthvī is described as both protecting Gautama Buddha and as being his witness for his enlightenment. Prithvi appears in Early Buddhism in the Pāli Canon, dispelling the temptation figure Mara by attesting to Gautama Buddha's worthiness to attain enlightenment. The Buddha is very frequently illustrated in figurative art wielding bhūmisparśa or "earth-touching" mudrā.
I haven't found it in the Pali cannon.
Various places though say that the story evolved, that people added to it or retold it; for example,
One element, however, is still not evident: Maara does not claim the seat on which the Bodhisatta is seated, and hence the need to call as witness the earth (or the earth-goddess, as the later versions have it) has not arisen.