Hidden mega-structures deep inside Earth may have been quietly steering our planet’s magnetic field—and rewriting what we thought we knew about Earth’s past.

The blobs lie at the base of Earth’s mantle, around 1,802 miles beneath Africa and the Pacific.

Scientists may finally be closing in on the origins of two colossal, mysterious structures buried nearly 1,800 miles inside Earth—hidden formations that have puzzled researchers for decades. New ...