Produced by: Manoj Kumar
Mega-buildings and dams like China’s Three Gorges Dam are subtly shifting Earth’s rotation. With its 40 billion cubic meters of water, the dam affects our planet’s spin, adding 0.06 microseconds to each day. This small change showcases the powerful impact of human-made structures on Earth’s delicate balance.
The Three Gorges Dam alters Earth’s “moment of inertia”—its resistance to spinning—by concentrating massive weight far from the center of rotation. Like adding weight to a spinning top, this change causes Earth’s rotation to slightly slow, showing just how megastructures impact our planetary mechanics.
Earth’s spin behaves like an ice skater extending or drawing in their arms. Just as the skater speeds up when compacted, Earth’s rotation adjusts based on mass distribution. Mega-buildings like Three Gorges function as if Earth’s “arms” are stretching outward, subtly slowing the planet down.
The Moon also plays a role in Earth’s rotation. Its gravitational pull creates tides, which gradually drain Earth’s rotational energy. Over centuries, this effect slows Earth by about 2 milliseconds per century, lengthening our days as lunar tides pull against Earth’s spin.
Human activity can sometimes speed up Earth’s rotation. The drying of the Aral Sea, which lost much of its water since the 1960s, increased Earth’s rotational speed over three times more than the Three Gorges Dam. Such impacts highlight the lasting influence of human intervention.
Major earthquakes can also alter Earth’s rotation. The 2011 earthquake in Japan sped up Earth’s spin by 1.8 millionths of a second, showcasing the significant force natural events exert on our planet’s rotation.
Earth’s rotation doesn’t just slow—it can also speed up. On June 29, 2022, Earth recorded its shortest day, spinning 1.59 milliseconds faster. Scientists link this anomaly to changes within Earth’s core, a reminder of our planet’s mysterious inner dynamics.
Massive shifts, like polar ice melt and mega-dams, can also nudge Earth’s poles. The Three Gorges Dam reportedly moves Earth’s poles by two centimeters, a shift slight yet detectable by scientists, showing how our constructions physically move the planet’s axis.
These tiny changes matter. Space agencies depend on precise Earth rotation data to navigate satellites and planetary probes. Megastructures, earthquakes, and tides all alter Earth’s spin just enough that scientists must continuously recalibrate to keep global navigation accurate.