When the Ice Is Gone

In 2018, lumps of frozen soil, collected from the bottom of the world's first deep ice core and lost for decades, reappeared in Denmark. When geologist Paul Bierman and his team first melted a piece of this unique material, they were shocked to find perfectly preserved leaves, twigs and moss. That observation led them to a startling discovery: Greenland's ice sheet had melted naturally before, about 400,000 years ago. The remote island's ice was far more fragile than scientists had realised-unstable even without human interference.