Superman need not worry that researchers at the University of Oregon are using radioactive krypton; they're just trying to determine the age of some Antarctic ice.

The inert gas -- not the fictional green substance kryptonite that is the nemesis of the Man of Steel -- could help scientists find and identify the oldest ice on Earth.

Some researchers believe some blue ice in Antarctica is around 2.5 million years old, and could be a possible source of clues about a puzzling gap in the climate history of our planet.

It was around that time the planet's cycles of cold and hot climate began a shift from period of 41,000 years to the modern cycle of 100,000 years, a shift science has yet to fully understand.

Researchers have studied ocean sediments of the period for clues, so far without success, and say finding ice old enough could help solve the mystery through atmospheric dust and cases locked inside.

 "There are interesting scientific questions we could answer if we had such old ice," says Christos Buizert, an Oregon State University paleoclimatologist.

Buizert is leading a study of blue ice in Antarctica, formed when mountains create a barrier to flowing ice and force it upwards, bringing much older ice close to the surface, making it possible to recover and analyze it.

The researchers say they only have to drill or dig 15 feet down from the surface to find extremely old ice untouched by the atmosphere of today.

"You can just chainsaw it up and have as much ice as you want, but the difficulty is figuring out how old it is," Buizert says.

It could be as old as 2.5 million years, but that's sometimes difficult to determine -- which is where the krypton comes in, the researchers say.

Analyzing rare isotopes of krypton imprisoned in air bubbles in samples can accurately identify extremely ancient Antarctic ice and give a date, they say.

That's because the decay rate of radioactive krypton and is isotopes is precisely known.

 "This new krypton method is the most precise way of telling us the age of this old ice," says Buizert, lead author of a study appearing in the Proceedings of the National Academy of Sciences.

The researchers say they hope to use the technique to find Antarctic ice much older than that found in ice core samples gathered to date.