They had been working on a tower that would be part of the western wing of Frog's castle for a couple weeks. The tower was about 30 feet tall, and Frog was busy pulling more large (very large) bricks to the top in a bucket on a rope, with another guy helping him. The other guy needed to go to the bathroom and left Frog holding the rope. Frog, being a light-weight, immediately flew upward, and the bucket downward. Frog hit the pulley at the top of the rope, knocking him out, just as the bucket hit the ground. The bucket's bottom broke off, and Frog, now heavier than the bucket, fell to the ground, and smashed his head on the bricks. He died.
Word soon arrived at Guardia Castle.
"He's... dead?" King Guardia choked, "We need to inform his friends and family."
"Well," one attendant said, "He has no family, and all his friends are, or will be, in 1000 and 2300 a.d."
"How will we inform them, if none of them will exist for another, 390 years, at least?"
"We could leave them a note and hope that it stays in the same place for 400 years," someone in the back suggested.
"How would that work?" someone else asked.
"Well, if the note stays in the same place for 400 years, and doesn't decay, and the ink doesn't bleach in the sun, and..."
"Okay, we get it. There's a lot of variables in there, but it's worth a try," King Guardia said.
So a plan was made to staple a note addressed to Crono, Marle, and Lucca into the ground, and to nail some Jell-O to a tree.