Turns out, the planet's crust tipped on its side and back again around 84 million years ago, in a phenomenon that researchers have dubbed a "cosmic yo-yo." .

The actual name for the tipping is true polar wander (TPW), which occurs when the outer layers of a planet or moon move around its core, tilting the crust relative to the object's axis.

Some researchers had previously predicted that TPW occurred on Earth late in the Cretaceous period, between 145 million and 66 million years ago, but that was hotly debated, according to a statement by the researchers.

They found that the planet tilted 12 degrees relative to its axis around 84 million years ago, before fully returning to its original position over the next 5 million years. .

"This observation represents the most recent large-scale TPW documented and challenges the notion that the [Earth's] spin axis has been largely stable over the past 100 million years," the researchers wrote in their paper, published online June 15 in the journal Nature Communications. .

Earth is made out of four main layers: the solid inner core, the liquid outer core, the mantle and the crust.

"What's actually happening is that the whole rocky shell of the planet [the mantle and crust] is rotating around the liquid outer core.".

Individual pieces of Earth's outermost layers are constantly moving and changing as tectonic plates collide together and subduct underneath one another; but during TPW, the outer layers move together as a single unit.

Some types of bacteria can create chains of tiny magnetite crystals, which naturally orient with Earth's magnetic field at the time of their creation.

Because Earth's crust moved during TPW, and not its magnetic field, these magnetic fossils (which remained in surface layers of the planet) revealed how much the crust moved relative to Earth's magnetic field over time

The team found that Earth's crust moved a total of almost 25 degrees over a period of 5 million years