U.S.-led scientists say they have found the last traces of tundra that grew in interior Antarctica before temperatures dropped millions of years ago.

The National Science Foundation-funded researchers said an abrupt, dramatic climate cooling during an approximately 200,000-year span -- a relatively brief period of geological time -- occurred about 14 million years ago, forcing the extinction of tundra plants and insects and transforming the Antarctic interior into a perpetual deeply frozen region.

The international team of scientists -- headed by David Marchant of Boston University and Allan Ashworth and Adam Lewis of North Dakota State University -- combined evidence from glacial geology, paleoecology, volcanic ash dating and computer modeling, to report the major climate change.

"It is one of the most dramatic and long-lasting changes that one can imagine," said Marchant. "I don't know of any other place on Earth where such an enduring change has been documented. The fact that it is associated with the extinction of tundra plants and insects helps provide quantitative estimates for the magnitude of this change."

The study that included scientists from Ohio State University and the University of Montana is detailed in the Proceedings of the National Academy of Sciences.