Watch MyFlixer. Ice has always moved. When glaciation took hold some 34 million years ago, interconnected rivers of ice combined to produce the Earth's vast ice sheets. As temperatures slowly warmed glaciers developed a unique balancing act; advancing and retreating to calibrate their annual winter accumulation against summer melt. Sometimes calving colossal icebergs into the sea. A positive feedback loop that has regulated the movement of ice for millions of years.