Two ice cores from the tropical Peruvian Andes reveal Earth's detailed tropical climate history year by year for nearly 1,800 years, researchers say.

Researchers at Ohio State University who retrieved the cores from a Peruvian ice cap in 2003 are calling them "Rosetta Stone" samples with which to compare other climate histories from Earth's tropical and subtropical regions over the last two millennia.

The scientists said they noticed startling similarities to other ice cores retrieved from Tibet and the Himalaya, with patterns in the chemical composition of certain layers matching up, even though the cores were taken from opposite sides of the planet.

"These ice cores provide the longest and highest-resolution tropical ice core record to date," earth sciences Professor Lonnie Thompson said.

"In fact, having drilled ice cores throughout the tropics for more than 30 years, we now know that this is the highest-resolution tropical ice core record that is likely to be retrieved."

The cores will provide a new tool for researchers to study Earth's past climate and better understand the climate changes that are happening today, the researchers said.

The new cores are special, the researchers say, because most of their 1,800-year history exists as clearly defined layers of light and dark: light from the accumulated snow of the wet season, and dark from the accumulated dust of the dry season.

The cores will provide a permanent record for future use by climate scientists, Thompson said.

"The frozen history from this tropical ice cap -- which is melting away as Earth continues to warm -- is archived in freezers at minus 30 degrees centigrade (minus 22 degrees Fahrenheit) so that creative people will have access to it 20 years from now, using instruments and techniques that don't even exist today," he said.