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Ur was a supercontinent that formed 3.1 billion years ago in the early Archaean eon (Mesoarchaean era). It might have been the oldest continent on Earth, half a billion years older than Arctica. However, it may have been preceded by one other supercontinent, Vaalbara, which might have formed about 3.6 billion years ago. Ur joined with the continents Nena and Atlantica about 1 billion to form the supercontinent Rodinia. Ur 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, Ur is considered to be 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 is about 1000 km too far south. When Ur was the only continent on Earth, all other land was in the form of small granite islands and small land-masses like Vaalbara, that were not large enough to be continents.
- ~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.
- Lerner, K. Lee; Lerner, Brenda Wilmoth, eds. (2003). "Supercontinents". Gale Cengage/eNotes.com. http://www.enotes.com/earth-science/supercontinents.
- Zubritsky, Elizabeth (1997). "In the beginning, there was Ur". Endeavors. http://endeavors.unc.edu/spr97/ur.html.
- Zimmer, Carl (January 1997). "In Times of Ur". Discover Magazine. http://discovermagazine.com/1997/jan/intimesofur987.