Formation of Earth's Inner Core (IMAGE) University of Rochester Caption A depiction of Earth, first without an inner core; second, with an inner core beginning to grow, around 550 million years ago; third, with an outermost and innermost inner core, around 450 million years ago. University of Rochester researchers used paleomagnetism to determine these two key dates in the history of the inner core, which they believe restored the planet’s magnetic field just before the explosion of life on Earth. Credit University of Rochester illustration / Michael Osadciw Usage Restrictions None License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.