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.
Ur joined with the continents Nena and Atlantica about 1 billion years ago to form the supercontinent Rodinia. Ur had survived as a single unit, until it was separated when the supercontinent Pangaea broke apart into Laurasia and Gondwana.