Ice cores from Antarctica could reveal information about Earth's climate and greenhouse gases extending as far back as 1.5 million years, researchers say.

Ice cores from newly identified regions could be almost twice as old as the oldest ice core drilled to date, they report in the journal of the European Geosciences Union.

Scientists say they hope to find clues to a significant climate transition that previous marine-sediment studies reveal happened some 1.2 million years to 900,000 years ago.

"Ice cores contain little air bubbles and, thus, represent the only direct archive of the composition of the past atmosphere," lead study author Hubertus Fischer of the University of Bern in Switzerland said.

"The information on greenhouse-gas concentrations at that time can only be gained from an Antarctic ice core covering the last 1.5 million years," he said. "Such an ice core does not exist yet, but ice of that age should be in principle hidden in the Antarctic ice sheet."

Researchers have been attempting to identify regions in Antarctica where ice sheets of such an age might exist.

"To constrain the possible locations where such 1.5 million-year old -- and in terms of its layering undisturbed -- ice could be found in Antarctica, we compiled the available data on climate and ice conditions in the Antarctic and used a simple ice and heat flow model to locate larger areas where such old ice may exist," study co-author Eric Wolff of the British Antarctic Survey said.

The researchers said they concluded 1.5 million-year old ice should still exist at the bottom of East Antarctica in regions close to the major Domes -- the highest points on the ice sheet -- and near the South Pole.

The next step, they said, is to survey the identified sites to measure ice thickness and temperature at the bottom of the ice sheet before selecting a final drill location.