Scientists have reported that a core drilled in Antarctica has yielded 2.7 million year old ice. Bubbles in the ice contain greenhouse gases from the Earth’s atmosphere at a time when glacial advance and retreat just had started, thus offering the potential to investigate what had triggered the ice ages. This makes the core the only sample of ancient Earth’s atmosphere at the time being.
Until now, the oldest icy climate record hailed from a core found at Dome C. With its help, scientists were able to retrace Earth’s climate history back around 800,000 years. According to Yuzhen Yan a graduate student from Princeton University, the new core revealed CO2 levels that were lower than 300 ppm, which is lower than today’s level. If these levels prove to be correct, paleoclimatologists will have to revise their models of what actually is needed to send the planet into an ice age. The discovery also offers a new area to search for the so-called «blue ice», a sort of Holy Grail for climatologists and geochemists. This kind of ice is considered especially old as it origins from largely unaffected areas of melting processes which usually happen on the deep bedrock of glaciers. A team of scientists led by Princeton University went after such a blue ice area in the Allan Hills, a region where the ice flows across rocky ridges and brings old, deep layers closer to the surface. In this area, strong winds strip away snow and young ice and leave the older tougher layers of compressed ice unattached.
To date the ice traditionally by determining the annual layers is confounded by the contortions of the topgraphy and the movement of the ice. Michael Bender, a Princeton geochemist, solved the problem by finding a way to date chunks of ice directly from trace amounts of argon and potassium gases. His technique, albeit not as precise as other methods, can date ice to within 100,000 years. The team used two attempts to come across the precious core. In 2010, a first attempt at the Allan Hills had revealed chunks of ice that were around 1 million years old, the first ice from a crucial time when glacial periods were switching from occuring every 40,000 years to every 100,000 years. Again, in 2015, the team returned to this site and was able to drill into the remaining ice to come out with the oldest ice known to date. Even though efforts to find ice of a similar age at other places are taken by other teams, they are unlikely to succeed. «In that sense, the Allan Hills ice core may stand on its own for some time», says John Goodge, a geologist from the University of Minnesota. But the Princeton team wants to beat the odds by going back and trying to drill even deeper to go back in time even before the ice ages. It is possible that they might succeed and bring back ice that is 5 million years old. This would offer a glimpse into a past when temperatures are thought to resemble what Earth is heading towards with human-driven warming.
Source: Paul Voosen, Science Magazine