a massive, kilometre-thick ice shelf once covered the entire Arctic Ocean during the coldest phases of the Ice Ages. A new study, now published in Science Advances , questions this idea. The research team found no evidence of such a permanent, pan-Arctic ice shelf. Instead, the Arctic Ocean appears to have been covered by seasonal sea ice, allowing open water—and life—to persist even [...] past 750,000 years. This discovery sheds new light on how the Arctic has responded to climate extremes in the past—and how it may evolve in the future.