Added 1 new A* page:I don't remember quite how this happened but anyway I recently came across the supercontinent cycle page on Wikipedia. Now we've probably all heard of Pangaea and all, but that was only the most *recent* supercontinent--there were loads of others before Pangaea! And the first supercontinent might've been one called Ur that formed about 3 billion years ago (although some might say Vaalbara preceded it by about 600,000,000 years, but Vaalbara was a tiny little thing maybe about the size of South Africa, whereas Ur was maybe close to the size of Australia, and, I dunno, you gotta draw the line somewhere, ya know?|
And Ur lasted right up until Pangaea broke up, leading to the modern continents--what was Ur is now in bits of Africa, Australia, and India. Here's the play-by-play from Wikipedia:
| ~3 billion years ago, Ur formed as the only continent on Earth.|
~2.8 billion years ago, Ur was a part of the major supercontinent Kenorland.
~2 billion years ago, Ur was a part of the major supercontinent Columbia.
~1 billion years ago, Ur was a part of the major supercontinent Rodinia.
~550 million years ago, Ur was a part of the major supercontinent Pannotia.
~300 million years ago, Ur was a part of the major supercontinent Pangaea.
~208 million years ago, Ur was torn apart into parts of Laurasia and Gondwana.
~65 million years ago, the African part of Ur was torn apart as part of India.
~Present, Ur is part of Australia and Madagascar.
Or, in a more general perspective given by this article (which also has a nice illustration showing these continental shifts):
|Rogers says Ur was the first continent, formed three billion years ago, followed by Arctica half a billion years later. Another half a billion years passed before Baltica and Atlantica emerged. The four continents roamed separately until, about one-and-a-half billion years ago, Arctica and Baltica collided with what is now eastern Antarctica to form Nena.|
When Nena, Atlantica, and Ur came together one billion years ago, the supercontinent Rodinia was born. After 300 million years, the three landmasses separated for about 400 million years, then came back together in a new configuration, Pangea.
Ur was more or less invented by University of North Carolina geologist John Rogers in 1996, when he pieced it together in a paper called "A History of Continents in the Past Three Billion Years," in which he noted that those bits of three current continents all dated back to about 3 billion years, and had been together in Pangaea--so that meant they were probably a continent that had existed by itself before the younger rocks around it.
I mostly just like the names some of these old continents have. "Ur" is nice, and I suppose Rogers just got that from the ancient Sumerian city-state of the same name. "Arctica" as named above is pretty nice, and there's also Atlantica. And all right, I guess Vaalbara is a pretty cool name, too.
Just a couple other interesting articles I saw linked from one of those sites: Alzheimers spreads like a virus from neuron to neuron is an interesting one from the A* neuroscience perspective, and then are you ready for Russians about to breach 20-million-year-old lake in Antarctica? Man there could be some crazy stuff in there.