UR was a supercontinent, on the Earth, that formed 3.1 billion years ago in the early Archaean eon (during the Mesoarchaean era). It might have been the oldest continent on Earth, half a billion years older than Arctica. However, one other supercontinent, Vaalbara, may have come before Ur. Vaalbara might have formed about 3.6 billion years ago. 