For over 60 years, the British Antarctic Survey (BAS) has been working to unlock secrets above and below the ice of the world's most remote continent.

In 1985, their scientists discovered thinning in the ozone layer over Antarctica, leading to global change in banning production of ozone-depleting chemicals.

They hope their latest discovery will offer valuable historical insights too, to help understand current changes in the earth's climate.

Working with a team of experts from 10 European countries, they have extracted the world's oldest ice cores, dating back between 1.2 and 1.5 million years.

The delicate process took place at Little Dome C, a field camp in East Antarctica. After scientists drilled a hole reaching 2,800 meters into the ice sheet, each 4.5 meter section of ice took around two and a half hours to recover.

The samples were split into smaller pieces, each carefully recorded before being shipped to institutions around Europe for analysis.

In all, 190 meters of ice came to Cambridge in the UK. They have been cut into meter-long sections, 3.5 centimeters square, ready to be tested; until then, they're kept safe at a temperature of -25 degrees Celsius.

"Some of the ice in here is from the very very bottom of the bore hole, so some of the very oldest ice," explains BAS ice core engineer James Veale. "This piece here – that I will very carefully pick up – is from about 2,600 meters down. It's at least 1.2 million years old.

"When you get this deep, and the ice is under this much pressure, it just looks like glass," he continues "There are very little occlusions, the bubbles of atmosphere are so small you can't even see them anymore."

How to analyze 1.2-million-year-old ice

Using a technique called continuous flow analysis, the team will analyze the samples, melting the ice millimeters at a time.

The dust, gases, isotopes and chemical signals discovered could give clues to past climate and environmental changes, including wind patterns, temperatures and rainfall.

One of the biggest questions this ancient ice could help answer is why Earth's natural climate cycles changed – very suddenly, by the standards of deep time.

Around 800,000 to 1.2 million years ago, the Mid-Pleistocene Transition changed the length of the planet's glacial cycles – that is, the transition from warmer eras to cold glacial times.  

These changes had been happening every 40,000 years but suddenly became much less frequent, happening only every 100,000 years. 

"This question of why did we change from a 40,000-year cycle to a 100,000-year cycle remains one of the biggest questions within our scientific field," says Dr Liz Thomas, BAS' Head of Ice Core Research. "What was it that caused that transition? And is it a potential analogue for how we may be changing in the future?"

The discoveries locked inside this ancient ice could reveal just how sensitive our climate is to human-driven change, like rising carbon dioxide levels.

In the weeks ahead, the melted ice will be analyzed. Its secrets, frozen for over a million years, may help shape the choices we make for our planet in the decades to come.