Science Daily — A sheet of molten rock roughly 10 miles thick spreads underneath much of the American Southwest, some 250 miles below Tucson, Ariz. From the surface, you can't see it, smell it or feel it.

But Arizona geophysicists Daniel Toffelmier and James Tyburczy detected the molten layer with a comparatively new and overlooked technique for exploring the deep Earth that uses magnetic eruptions on the sun.

"We had two goals in this research," says Tyburczy. "We wanted to test a hypothesis about what happens to rock in Earth's mantle when it rises to a particular depth -- and we also wanted to test a computer modeling technique for studying the deep Earth."

He adds, "Finding that sheet of melt-rock tells us we we're on the right track."