Ice cores drilled from Antarctica have revealed a brief but remarkably warm period in the continent’s history. Scientists are now trying to figure out what caused the warm spell and how knowing about it will affect current climate change modeling.

The clue revealed in the ice core was a two-meter ( 6.5 feet) layer of fossil content, rich in marine algae and pollen. At first, researcher Sophie Warny of Louisiana State University (LSU) thought the core samples might have been contaminated or have been sent from another location by mistake.

Neither was true. The sample showed that a brief but rapid period of warming occurred in Antarctica about 15 million years ago, but lasted for only thousands of years. This event took place during the Middle Miocene Climate Transition when temperatures around the globe dropped. The microfossils may help researchers discover how Antarctica responded to global warming earlier and offer clues to how the continent might react in the future. The ice core came to the LSU Museum of Natural Sciences from the Antarctic Geological Drilling Program  (ANDRILL), which provides core samples to an international team. According to a release from LSU, Warny called her colleagues when she saw the unusual abundance of microfossils in her sample. Later meetings and separate tests confirmed that indeed the core revealed an unusual event in the continent’s climate history. The fossils indicate that land temperatures on Antarctica may have been as warm as 50 degrees Fahrenheit. Woody plants might have been able to grow on the continent. An increase in meltwater from glaciers and rainfall could have reduced the sea ice. The estimated sea surface temperatures ranged between zero and 11 degrees Celsius.

Records from other parts of the globe have recognized the Middle Miocene Climate Transition, but now researchers have information about its occurrence in Antarctica and a better understanding of ice sheet behavior when temperatures rise. Warny, assistant professor of geology and geophysics at LSU, points out that the microfossils “provide us with quantitative data of what the environment was actually like in Antarctica at the time, showing how this continent reacted when climatic conditions were warmer than they are today.”