An ancient slab of seafloor that was around when Earth’s earliest known dinosaurs emerged, has been discovered beneath the Pacific Ocean, where it has seemingly hovered in a sort of mid-dive for more than 120 million years.

In addition to illuminating geological processes deep inside Earth, the cold, descending slab of dense rock, located some 410 to 660 kilometers below the planet’s surface, could explain a mysterious gap between two sections of a giant blob in the mantle layer.