China's Three Gorges Dam is so massive that it actually slows down the Earth's rotation.

In 2005, a NASA scientist named Dr. Richard Gross calculated exactly how this happens. The dam creates a giant lake that is 600 kilometers long. When this lake is full, it lifts 42 billion tons of water about 175 meters into the air. This moves a huge amount of weight further away from the Earth's center.Think of a figure skater spinning on ice. When they pull their arms in tight, they spin very fast. When they stretch their arms out wide, they slow down. This is a rule of physics called 'angular momentum.' By lifting all that water higher up, the dam acts like the skater's outstretched arms, causing the Earth to slow its spin.Because of this shift, every single day on Earth became 0.06 microseconds longer. A microsecond is one-millionth of a second, so it is way too fast for humans to feel. However, super-accurate atomic clocks can measure it. The shift was even strong enough to move the Earth’s North and South Poles by about 2 centimeters.The amount of water held by the dam weighs as much as 100,000 Empire State Buildings. It is one of the only things humans have ever built that is heavy enough to change how our entire planet moves through space.