About 3,200 miles down towards the center of the Earth, there is an iron-nickel ball about 760 miles in radius. Though the temperature at that depth is very high—about 5,400 degrees celsius, nearly as high as the surface of the sun and 3.5 times the temperature necessary to melt the metal at the Earth’s surface—the ball is solid due to the tremendous pressure from the mass of the rest of the Earth.

This is the Earth’s inner core, the deepest of our planet’s geologic layers—at the center of the depiction here, via the Wikipedia user and vector artist Kelvin Song:

But new research from geologists at Nanjing University and the University of Illinois published in Nature Geoscience suggests that there might actually be an inner-inner core—a part even closer to the center of the core, with dramatically different properties than the rest of the inner core.

The difference is in the alignment of the molecules in the metal. The research suggests that in the inner core we already knew about, those molecules form a crystal structure aligned along a north-south axis that points toward the north and south poles. In the inner-inner core, however, the crystals appear to be aligned along an axis through the equator that points toward Central America and Southeast Asia.

This alignment difference could have been caused by a 90-degree rotation in the Earth’s magnetic field 500 million years ago, Simon Redfern of the University of Cambridge told the BBC.

In other words, heading north back then might have meant going toward what we now know as Guatemala.