Scientists confirm liquid water on early Earth
Scientists have found that the Earth had formed patterns of crust formation, erosion and sediment recycling as early as 4.35 billion years ago. Their findings came during a study of zircon crystals formed during the earliest period of Earth's history, the Hadean Eon (4.5 billion to 4.0 billion years ago).
Full article at Spaceflight Now
Now that's interesting. The first thing that came to mind was one theory of how our moon was formed. With water that early on Earth and 4.5 million year old dry moon rocks it just how old was Earth when the impact occurred?