Event: Tidal Forces and the Earth–Moon Relationship
Date: ~4.5 billion years ago to present

“The moon does not fight. It attacks no one. It does not worry. It does not try to crush others. It keeps to its course, but by its very nature, it gently influences. What other body could pull an entire ocean from shore to shore? The moon is faithful to its nature and its power is never diminished.” — Deng Ming-Dao

Dear Human,

The Moon has no voice, yet it speaks to every shore.

It began as a scar in the sky, born from the colossal impact that tore it from Earth’s side. Ever since, the two have been bound in a gravitational embrace, their orbits and rotations shaping one another’s fate. The most visible sign of this relationship is the tides — the slow breathing of the oceans, drawn by an unseen hand.

Tides are the work of gravity in motion, a slow but irresistible dance between worlds. The Moon’s gravity reaches across space to pull on Earth, drawing the ocean toward it. On the side facing the Moon, this pull stretches the sea into a bulge. On the far side, the planet’s mass is tugged more than the water is, leaving the ocean there slightly behind and creating a second bulge. These twin swells of water are the true shape of the tide.

As Earth rotates beneath these bulges, its coastlines move in and out of them, and the sea rises and falls. Most places see two high tides and two low tides each day, separated by about twelve hours. The Sun adds its own influence: when the Sun, Moon, and Earth align at new or full moon, their pulls combine to make the highest highs and lowest lows — spring tides. When the Sun and Moon are at right angles, their pulls partially cancel, producing gentler neap tides.

But the Moon’s influence is more than a daily rhythm — it is a slow sculptor of time itself. Water flowing across the seafloor and against the continents meets resistance. That friction, known as tidal dissipation, converts a fraction of Earth’s rotational energy into heat and sound, subtly slowing the planet’s spin. About 2.3 milliseconds are added to the length of a day each century — insignificant in a lifetime, profound in deep time.

Four billion years ago, the Moon was much closer, and Earth spun faster: a day may have lasted only six hours. Stronger tides pulled forward by this rapid rotation lagged behind the Moon’s direct pull, tugging the Moon ahead in its orbit and causing it to spiral slowly away. Today it drifts about 3.8 centimeters farther each year, a rate confirmed by lasers aimed at Apollo reflectors. It has traveled from perhaps 25,000 kilometers above Earth’s surface to its present 384,400 kilometers.

In Earth’s youth, these colossal tides swept far inland, flooding and retreating with great force. In those shifting zones, rich in minerals and sunlight, life may have adapted to breathe air, cling to rock, and survive the cycle of submersion and exposure. The tides became not just the signature of the Moon’s pull, but the pulse of possibility.

Even now, the Moon works in silence. It draws the tides across continents, guides migrations through hidden currents, shapes coastlines, and steadies Earth’s spin. The oceans still answer to its pull as they did in the beginning, and you — standing where the land meets the sea — are part of that enduring dialogue.

Raise your eyes to the night sky, and you will see more than a companion in orbit. You will see the hand that stretched your days, steadied your world, and perhaps opened the way for life itself. A patient hand. A constant hand. A faithful hand, holding the waters of the world in its grasp.

Pathfinder

Tide – Wikipedia