From Science:
Scientists announced [August 15, 2017] that a core drilled in Antarctica has yielded 2.7-million-year-old ice, an astonishing find 1.7 million years older than the previous record-holder. Bubbles in the ice contain greenhouse gases from Earth’s atmosphere at a time when the planet’s cycles of glacial advance and retreat were just beginning, potentially offering clues to what triggered the ice ages. That information alone makes the value of the sample “incredible,” says David Shuster, a geochemist at the University of California, Berkeley, who is unaffiliated with the research. “This is the only sample of ancient Earth’s atmosphere that we have access to.”
Described at the Goldschmidt Conference in Paris by Yuzhen Yan, a graduate student at Princeton University, the ice revealed atmospheric carbon dioxide (CO2) levels that did not exceed 300 parts per million, well below today’s levels. Some models of ancient climate predict that such relatively low levels would be needed to tip Earth into a series of ice ages. But some proxies gleaned from the fossils of animals that lived in shallow oceans had indicated higher CO2 levels. If the new result holds up, says Yige Zhang, a paleoclimatologist at Texas A&M University in College Station, the proxies will need to be recalibrated. “We have some work to do.”
The discovery also points the way to finding even older ice, because it comes from a largely ignored “blue ice” area, where peculiar dynamics can preserve old layers. Although blue ice areas offer only a fragmentary view of the past, they may turn into prime hunting grounds for ancient ice, says Ed Brook, a geochemist on the discovery team at Oregon State University in Corvallis. “Ice that’s this old really makes people stand up and notice,” he says. “We’re just scratching the surface.”