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.
In the early period of Ur's existence, it was probably the only continent on Earth. Therefore, scientists call Ur a supercontinent, even though it was probably smaller than Australia is now. Today's New Zealand is similar to Ur, but rotated 90 degrees out of phase, and about 1,000 kilometres (620 miles) too far south.
- About 3.1 billion years ago, Ur formed as the only continent on Earth.
- ~2.8 billion years ago, Ur was a part of the supercontinent Kenorland.
- ~2 billion years ago, Ur was a part of the supercontinent Columbia.
- ~1 billion years ago, Ur was a part of the supercontinent Rodinia.
- ~550 million years ago, Ur was a part of the supercontinent Pannotia.
- ~300 million years ago, Ur was a part of the supercontinent Pangaea.
- ~208 million years ago, Ur was separated into parts of Laurasia and Gondwana.
- ~65 million years ago, the African part of Ur was separated as part of India.
- Today, Ur is part of Australia and Madagascar.