quietly sitting
I touch the ground-
space dust

When Mara challenged Siddhartha as saying the he the title of Buddha “enlightened one” belonged to him his minions shouted that they testified for Mara.

Mara asked Siddhartha who would witness for him he reached out his right hand touched the earth, then the earth itself spoke: “I bear you witness!”
At this Mara disappeared.
Siddhartha Gautama reached enlightenment and became a Buddha.

I think that Earth Day is an excellent time to think about how we all came from the Earth and will return to it one day. A step further is to remember the Earth formed from stardust and to it we all will return.
Therefore the universe can testify on our Buddha nature.