The Moon-forming impact

A body often called Theia strikes Earth a glancing blow, vaporising much of both and throwing a disk of molten rock into orbit that coalesces into the Moon within perhaps a century. The impact re-melts Earth entirely, sets its axial tilt and leaves it spinning with a day only a few hours long. Dating remains contested: lunar zircons point to 4.51 billion years, while a cluster of 4.35-billion-year lunar rock ages was long read as the formation age and is now argued to record a later tidal remelting instead.