What is it?

Harold knows nearly everything. Just ask him. Unfortunately, Bennie
frequently does. "What's this?" she recently wanted to know, showing
Harold an object she had found on the front porch. Harold instantly
identified the object as part of a fossilized space ship which had
transported alien bacteria to Earth during the Devonian era. Scarring
on the dorsal fin indicated that the ship had been damaged by Earth's
air defense system. The bacterian colonists had been killed in the
resulting crash and only this single fragment of the ship had survived,
prompting Bennie, ages later, to another futile attempt to confound
Harold.