Longtime listeners to Blue Dot know that Dave has a lifelong fascination with the Moon from its exploration to its role in eclipses. But how did our companion world come to be? Since the Apollo missions brought back lunar samples, the most accepted idea is called the "Giant Impact Hypothesis" but the notion has its flaws -- mainly that if a Mars-sized object actually did hit the Earth and create the Moon, where is the evidence in the Moon rocks which are isotopically identical to Earth's?