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The Earth-Moon system evolves through tidal interactions: the Moon recedes from Earth at ~3.8 cm/year, Earth's rotation slows, and angular momentum is conserved. The Moon is tidally locked (always facing Earth), and its gravity drives tides in Earth's oceans and crust. This system exemplifies tidal evolution in any gravitationally coupled pair.
From your study of tidal forces and tidal locking, you know that gravitational gradients across an extended body produce tidal bulges, and that friction between these bulges and the body's rotation drives long-term orbital evolution. The Earth-Moon system is the most accessible example of this process in action, and it has been evolving since the Moon's formation roughly 4.5 billion years ago — most likely from a giant impact between the proto-Earth and a Mars-sized body called Theia.
The key mechanism is tidal friction. Earth rotates faster than the Moon orbits (a day is shorter than a month), so Earth's tidal bulges are carried slightly ahead of the Earth-Moon line by rotational drag. This offset means the Moon's gravity pulls back on the bulge, slowing Earth's rotation, while the bulge's gravity pulls the Moon forward in its orbit, adding energy and causing the Moon to spiral outward. The numbers are measurable: Earth's day lengthens by about 2.3 milliseconds per century, and laser ranging off retroreflectors left by Apollo astronauts confirms the Moon recedes at 3.8 cm per year. The total angular momentum of the system — Earth's spin plus the Moon's orbital motion — is conserved; what Earth loses in rotational angular momentum, the Moon gains in orbital angular momentum.
Tidal locking is the end state of this dissipation process for the smaller body. The Moon reached it long ago: tidal friction slowed the Moon's rotation until its spin period matched its orbital period, so it always presents the same face to Earth. Earth is on the same trajectory but much further from completion — billions of years from now, Earth's day would lengthen to match the lunar month if the system were left undisturbed. At that point, Earth and Moon would be mutually locked, always facing each other, like Pluto and Charon today.
The Moon's tidal influence extends well beyond ocean tides. It raises solid-body tides in Earth's crust (vertical displacement of ~30 cm), affects Earth's obliquity stability by acting as a gravitational anchor, and drives tidal heating in Earth's interior. The Moon also stabilizes Earth's axial tilt near 23.5°, preventing the chaotic obliquity swings that Mars experiences. This stabilization has profound implications for Earth's climate history and habitability — without the Moon, seasonal extremes could vary wildly over millions of years, potentially disrupting the conditions that allowed complex life to develop.