The outer core is liquid, the inner core is solid. That’s the way Earth has been depicted in textbooks for the past 66 years. But the work of Adam Dziewonski, Frank B. Baird Jr. Professor of Science, and graduate student Miaki Ishii shows that this picture doesn’t get to the bottom of things. Engulfed in the inner core, like a pit in a peach, lies a 360-mile-wide inner inner core. This core within a core within a core makes up one ten-thousandth of the Earth’s volume. Dziewonski and Ishii patiently examined records of hundreds of thousands of earthquake waves that passed through the center of the planet in the past 30 years to make the discovery. “It may be the oldest fossil left from the formation of Earth,” says Dziewonski. “Its origin remains unknown, but its presence could change our basic ideas about the origin and history of the planet.” Dziewonski and Ishii published their results in the Oct. 1, 2002 issue of the Proceedings of the National Academy of Sciences.