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Colorado Plateau

Ancient Earth not matching up

Everyone loves a good mystery. There’s nothing quite as good as sitting down, and trying to work out whether it actually was the butler, or if poor Jeeves was simply framed. But mysteries come in all shapes and sizes, as can be attested to by researchers from the University of Michigan and the University of Nebraska-Lincoln.

For the last 25 years or so, geoscientists and paleomagnetic records have combined to show that what is now the Colorado Plateau, shifted more than 1,300 miles north as part of the supercontinent Pangea, during a 100-million-year span. This is believed to have happened during the early Jurassic Period, when Pangea began to break up; ending about 200 million years ago.

However new evidence has presented a ‘conundrum’ to scientists.

“It’s a puzzle, a ‘conundrum’ is the word we like to use,” said Robert Oglesby of UNL. “And in the Science paper, we’re not solving the conundrum, we’re raising the conundrum.”

The ‘conundrum’ centers around research conducted by UNL researcher David Loope, focused in the Colorado Plateau. Loope, who is an expert on dune formation, found that from central Wyoming into central Utah, the region’s sandstone formations had preserved ancient dunes from 300 million to 200 million years ago.

The problem though, was that all these dunes were facing southwest, meaning that the winds over that large area were almost constantly from the northeast.

His study continued, and as the data continued to come in, he discovered that the direction of the dunes shifted to the southeast, in what is in modern days, now Utah. This meant that the winds had shifted to the northwest, and that these prevailing winds were consistent over a period of 100 million years.

Subsequently, all the information presented adds up to only one conclusion: that that area was at the equator.

“I thought that was very curious,” Loope said. “It didn’t seem to fit with what we think we know about where the continents were.”

Along with his UNL co-authors Oglesby and Clinton Rowe, Loope tried to find a computer model that would account for the new information.

“We ran the model in any different number of configurations just to see if we could make it do something different,” Rowe said. “It didn’t matter what we did to it, as long as you had some land, and it was distributed north and south of the equator, you would end up with this monsoonal flow that matched these records from the dunes.

“The equator is the only place you could get this large-scale arc of winds that turn from the northeast to the northwest as they moved south. Nowhere else would you get that as part of the general circulation unless the physics of the world 200 million years ago was very different from what it is today. And we just don’t think that’s the case.”

Enter U-M geophysicist Rob Van der Voo. A paleomagnetic expert, his field of study allows for scientists to determine the direction of the Earth’s magnetic field at a certain time in history. The records provided, showed that the area in question – the Colorado Plateau – moved from the equator to about 20 degrees north latitude from 300 million years ago to 200 million years ago.

“We brought Rob in to try to see if he could help us sort it out, and he’s like, ‘Gosh, guys, I don’t know. This is a conundrum,’” Oglesby said. “It’s important to note that we have not just a paleomag person as a co-author, but arguably the best-known paleomag person in the world—and he’s as confused as we are.”

“The nicest thing would have been if we had a solution, but we don’t,” said Van der Voo, the Frank H. T. Rhodes Professor of Geological Sciences at U-M. “All we can say is that we have this enigma, so perhaps our model of Pangea for the period in question is wrong or the wind direction didn’t follow the common patterns that we recognize in the modern world. Neither seems likely, but we’re bringing this inconsistency to the attention of the scientific community in hopes of stimulating further research.”

The team will continue to keep coming up with ideas, and presenting them to the computer model. But, for now, they are stumped. It is, in all senses of the term, a mystery.