"The details of this big event are still a bit of a mystery, but we've added another piece of the puzzle when ... models of Earth's structure. The presence of an innermost layer has been suspected ...

Imagine if Earth's history had a mystery novel, and one of its biggest unsolved puzzles was: Where did all the nitrogen go?

Researchers are now trying to understand the "innermost inner core" of the Earth by studying how seismic waves travel through ...