By trade, geologists display a rather cavalier attitude toward the continents. In their minds or on computer screens they frequently rearrange the world, shuffling about Africa and Asia faster than an interior decorator might move sofas. But even those long accustomed to the game of continental twister are doing a double take at a novel theory about Earth's ancient history Two researchers propose that North America and Antarctica once lay side by side, locked together in a marathon union spanning perhaps more than a billion years. think it's pretty surprising to most people. When I first told it to a colleague of mine, he told me I was out of my mind, says Ian WD. Dalziel, a geologist at the University of Texas in Austin and one formulator of the new theory Dalziel and Eldridge M. Moores, from the University of California, Davis, devised independent versions of the hypothesis after Moores visited Antarctica in 1989 on a field trip led by Dalziel. Plate tectonic experts have long suspected that most of Earth's continents combined to form a giant landmass, existing from about 800 to 600 million years ago, the end of the Precambrian time. The details from that far back remain fuzzy Yet geologists know that when the unnamed supercontinent splintered apart, some landmass separated from North America's western edge, which at the time ran through the present locations of Montana, Idaho and Nevada. The popular theory among researchers holds that the missing block of continent now forms Siberia. Moores and Dalziel believe East Antarctica makes a better candidate for North America's long-lost mate, despite the incredible distance now separating the two. They proposed this connection after noticing that certain rocks from the frozen continent bear a close resemblance to those found in parts of the United States. According to Moores, the Dronning Maud Land section of East Antarctica contains a band of 1.1-billion-year-old metamorphic rocks very similar to the so-called Grenville belt that runs from Texas through the Adirondack Mountains of New York and into Quebec. He suggests that Dronning Maud Land originally sat next to present-day Texas, forming a continuation of the Grenville province into Antarctica. If the ancient core of Antarctica was indeed wedded to early North America, the marriage may have lasted for an unusually long time, even by geologic standards. Similar rocks found in Arizona and Antarctica indicate the two continental cores got hitched at least 1.6 billion years ago. Locked together, they wandered the Earth as a unit for hundreds of millions of years and then joined up with other regions to form the late Precambrian supercontinent. North America would have finally divorced from Antarctica about 600 million years ago, when an ocean opened between the two continents. In Dalziel's view of the ancient world, Antarctica and North America both connected to Australia, which then bordered what is now northwest Canada (see map). After those western connections developed, the eastern side of North America bonded with ancient parts of South America. Dalziel describes North America as a keystone at the center of the late Precambrian supercontinent, which apparently straddled Earth's equator. Moores and Dalziel are not the first to suggest a connection between the polar continent and North America. More than a decade ago, Canadian geologists proposed a similar idea but never developed the concept, which lay fallow for many years until Moores and Dalziel developed it independently in separate papers, which will appear respectively in the May and June issues of GEOLOGY. The two researchers discussed their work last month at a meeting of the Geologic Society of America in San Francisco.