I thought this dvar torah was prudent, at least for Ames original question. It was taken from yutorah.org:
Shamayim and Eretz are obviously not equipped to serve as witnesses; what did Moshe intend by invoking them as such?
Again, Heaven and Earth are again likened to organic, thinking beings. How can Shamayim and Eretz, which are lifeless and have no desires, serve as examples and provide standards for living humans, who have brains, freedom, passions and inclinations?