Dating Earth's Core

Earth began as a ball of melted rock 4.5 billion years ago. Over time, the planet cooled into layers. One layer is the inner core—a ball of solid iron at Earth’s center. To learn more about when this layer may have formed, geologist Afu Lin modeled the conditions of the inner core in his lab at the University of Texas at Austin.

To mimic the pressure inside Earth, Lin’s team squeezed a sample of iron between two diamonds. Then they shined a laser, or concentrated beam of light, at the iron until it reached 2,727°C (4,940°F). By measuring how well the iron gave off heat, they were able to calculate how long it likely took for Earth’s core to cool and solidify. The results suggest that the inner core is about 1 billion years old.