Photograph courtesy Ian Dalziel
Published August 15, 2011
About 1.1 billion years ago, what are now El Paso, Texas, and Antarctica appear to have existed side by side, scientists say.
The find is part of a decades-long effort to piece together fragments of an ancient supercontinent that existed before Pangaea.
"Most people are familiar with Pangaea," said study co-author Staci Loewy, a geochemist at California State University, Bakersfield. "That was a supercontinent that formed 300 million years ago."
(See "Supercontinent Pangaea Pushed, Not Sucked, Into Place.")
Pangaea began to break apart about 225 million years ago due to geological processes related to plate tectonics, which eventually spread Earth's landmasses into the continents we see today.
The supercontinent's pieces can be reassembled by tracing ancient mountain belts and other geologic patterns—such as the Appalachian Mountains, which are geologically related to mountains of England and Scandinavia.
But "we see older mountain belts suggesting that all the continents came together in the past to make other supercontinents," Loewy said.
Some of these features appear to be traces of Pangaea's predecessor, Rodinia, a supercontinent that contained most of the word's landmasses from about 1.1 billion to 750 million years ago. (Also see "Earliest Animals Were Sea Sponges, Fossils Hint.")
Rock Matches "Such a Neat Thing"
For their study, Loewy and colleagues collected rocks from a region known as the North American Mid-continental Rift System.
The system is an ancient volcanic zone running from Canada to Texas, where what is now North America started to tear apart 1.1 billion years ago. The southern end of this rift includes the Franklin Mountains near El Paso.
The team then compared the North American rocks to samples from mountains in Coats Land in East Antarctica, on the coast of the Weddell Sea (map). The Coats Land mountains are mostly buried in ice, except for "two tiny tips of mountain peaks," Loewy said.
Rocks collected from both sites match in age and in lead isotope ratios, Loewy said, showing that both sets of volcanic rocks erupted from the same rift zone.
The results indicate that, even though the regions today are widely separated, the two landmasses were once connected.
"It's such a neat thing," she said, referring to the past ties between the West Texas desert and Antarctica's glaciers. "It's a quite spectacular contrast."
(Related: "Slimmer Indian Continent Drifted Ten Times Faster.")
Supercontinents Came in Cycles
Meanwhile, the search goes on for similar connections between fragments of other now vanished supercontinents. (Related: "Oldest Rocks on Earth Discovered?")
"There are people who have put forth models of earlier supercontinents. One, called Columbia, [may have] existed from 1.8 to 1.5 billion years [ago]," Loewy said.
"And at 2.4 to 2.6 billion years ago, there seems to have been another major event," she said. "There appear to have been multiple cycles throughout time."
The Texas-Antarctica connection is described August 5 in the online edition of the journal Geology.
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