http://www.sciencemag.org/news/2019/10/world-s-oldest-ice-core-could-solve-mystery-flipped-ice-age-cycles

Researchers endured bitter winds to collect the ancient ice in 2015.

In some ways, drilling into Antarctica’s ancient ice is easier than interpreting it. Today, more than 2 years after presenting the discovery of the world’s oldest ice core, scientists have published an analysis of the 2.7-million-year-old sample. One surprising finding: Air bubbles from 1.5 million years ago—from a time before the planet’s ice age cycles suddenly doubled in length—contain lower than expected levels of carbon dioxide (CO2), a possible clue to the shift in the ice age cycle.