Lunar rocks brought a puzzle: their age is 4.35 billion years, but the Moon itself should have appeared 150 million years earlier. The missing time is hidden in tidal heating. When the Moon hung closer to Earth, Earth's gravity acted like tireless hands: it constantly kneaded and bent the satellite. From this, heat was generated inside — just like in a rapidly bending wire. The nature of these forces was unraveled by Isaac Newton. For a full 150 million years, the lunar ocean of magma would not solidify, kept warm by this cosmic workout. But as soon as the magma began to thicken, tidal heating weakened, and the last drops of liquid rock snapped into solid in an instant. That is the moment we mistakenly consider the Moon's birth. In reality, lunar rocks merely recorded the final exhalation of its internal heat. This also explains the difference between the near and far sides of the Moon: cooling happened unevenly. And today, the same hellish heating melts the interior of Io — Jupiter's moon, making it the most volcanic body in the system.
The two sides of the Moon are like two different worlds: the near side has smooth dark 'seas', while the far side is a chaos of mountains and craters. It turns out tidal heating is to blame: it made the magma solidify unevenly.