Days on Earth are changing length

Scientists have recorded small variations in Earth's day length for decades. These changes are minuscule, sometimes just a few milliseconds, but they point to a shift in the planet's rotation speed.

Multiple forces affect Earth's spin

Fluctuations in the atmosphere and oceans can speed up or slow down rotation. Major earthquakes redistribute the planet's mass. Melting continental ice deposits water into oceans, also affecting rotation.

The deep Earth holds the answer

Beneath the rocky mantle lies the outer core, a one thousand four hundred mile thick layer of ultra-hot liquid metal in constant motion. As these flows change, they alter the planet's rotation speed.

Gravity creates a hidden mechanism

A new study in Nature proposes that the inner core's gravity pushes rotation in one direction while other core-mantle interactions oppose it. This gravitational competition, accumulated over decades, causes small changes in Earth's spin.

The inner core wants alignment

The inner core rotates at a different rate than the rest of the planet, becoming misaligned with mass irregularities in the mantle. Gravity tries to pull the layers back into alignment, which minutely influences the planet's surface rotation.

“the core "wants to be aligned"”

The model explains decades of data

Researchers reconstructed how inner core gravity influenced Earth's spin between nineteen sixty-four and two thousand nineteen. Their model closely reproduced both the timing and magnitude of observed gradual changes, though other unknown factors likely remain involved.

“gravity still wins”