From your balcony, the Moon looks eternal. Same glow. Same familiar face. It rises, sets, and hangs in the night sky with a confidence that feels permanent. Yet behind that calm presence, a slow, invisible change is unfolding—one that has been quietly reshaping Earth for billions of years and will continue long after humans are gone.
The Moon is moving away from us.
Not dramatically. Not enough to notice in a lifetime. But enough to lengthen our days, weaken our tides, and subtly alter the rhythms that have guided oceans, coastlines, and life itself since long before the first animals crawled onto land.
When the Moon was closer, Earth spun faster
To understand what’s happening now, you have to imagine a very different Earth.
Seventy million years ago, near the end of the dinosaur era, a day did not last 24 hours. It was closer to 23 hours and 30 minutes. The Sun still rose and set, seasons still changed, but the planet spun a little faster, squeezing more days into each year.
This isn’t guesswork or science fiction. Earth’s deep past keeps surprisingly precise records of time.
Certain ancient shellfish—now fossilised—grew in daily layers, much like tree rings. Each thin line marked one sunrise. By counting those layers and grouping them into yearly cycles, scientists can calculate how many days once fit into a year.
One famous study examined an extinct bivalve called Torreites sanchezi. Fossils from the late Cretaceous period revealed about 372 daily growth layers per year. Same year length. Shorter days. A faster-spinning Earth.
Go back further still, and the differences become extreme.
The violent birth of the Moon and colossal tides
Around 4.5 billion years ago, shortly after Earth formed, a Mars-sized body likely slammed into the young planet. The impact blasted debris into orbit, which eventually clumped together to form the Moon.
At first, the Moon was much closer—so close it would have dominated the sky, appearing several times larger than it does today. Its gravitational pull on Earth’s oceans was enormous. Tides weren’t gentle rises and falls along beaches; they were planet-shaping forces.
Those early tides:
- Reached far inland
- Mixed oceans intensely
- Converted huge amounts of Earth’s rotational energy into heat
Earth spun rapidly. The Moon tugged hard. And the long gravitational conversation between the two bodies began.
Why the Moon is drifting away today
Right now, the Moon is receding from Earth at about 3.8 centimetres per year—roughly the speed at which fingernails grow.
We know this with astonishing precision thanks to a clever experiment. Astronauts left small reflective mirrors on the Moon’s surface during the Apollo missions. Scientists on Earth fire laser pulses at these mirrors and measure how long the light takes to return. Even a change of a few millimetres shows up in the timing.
The reason for this drift isn’t mysterious. It’s written in the tides.
How tides push the Moon outward
The Moon’s gravity raises two broad bulges of ocean water on Earth—one facing the Moon, one on the opposite side. But because Earth rotates faster than the Moon orbits, those bulges don’t sit perfectly beneath the Moon. They’re dragged slightly ahead.
That tiny offset matters.
The bulges, packed with mass, pull on the Moon. Because they’re slightly ahead of it, they act like a gravitational push, transferring energy to the Moon’s orbit. The Moon gains energy and moves outward into a higher, wider path.
Earth pays the price.
That energy comes from Earth’s rotation. Friction between tidal currents and the seafloor—especially around continental shelves—converts rotational energy into heat. As a result:
- Earth’s spin slows
- Days grow longer
- The Moon drifts farther away
It’s a slow but relentless exchange.
What this means for the length of a day
The effect on your daily life is microscopic. Right now, Earth’s day lengthens by about 1.7 milliseconds per century due to tidal friction.
You won’t feel it. Your phone won’t notice. Your alarm clock doesn’t care.
But over geological time, those milliseconds stack up.
- Hundreds of millions of years ago: days were nearly an hour shorter
- Today: 24 hours
- Hundreds of millions of years from now: days will exceed 24 hours
Time itself hasn’t changed—but how Earth parcels it into days has.
Softer tides, quieter coasts (very slowly)
Distance matters for gravity. As the Moon moves away, its pull weakens. That means tides gradually lose strength.
High tides won’t rise as high. Low tides won’t drop as far. The difference between them—the tidal range—shrinks.
This doesn’t mean beaches will suddenly calm or oceans will stop moving. The change is glacially slow. But over millions of years, weaker tides can reshape coastlines and ecosystems.
Tides:
- Flush estuaries
- Deliver nutrients
- Signal feeding and breeding cycles for marine life
As tidal energy fades, these processes subtly shift. Coastal erosion patterns change. Sediment settles differently. Some habitats expand while others contract.
Tides are not just water moving—they are an ecological engine. And the Moon is slowly turning the dial down.
Tides, oceans, and climate connections
Tides also help stir the oceans, mixing warm surface water with colder depths. This mixing influences how heat and nutrients circulate globally.
Stronger tides promote vigorous mixing. Weaker tides can allow stratification—layers of water that don’t mix as easily.
Over millions of years, changes in tidal mixing can interact with:
- Plate tectonics
- Ocean basin shapes
- Atmospheric greenhouse gas levels
The Moon’s retreat doesn’t drive climate on its own, but it quietly influences the background conditions under which climate systems operate.
Will Earth ever become tidally locked?
The Moon already is. It rotates once per orbit, always showing us the same face—a state called tidal locking.
In theory, Earth could eventually reach a similar state, rotating once per lunar orbit so that the same side always faces the Moon.
If that happened:
- Tidal friction would drop sharply
- The Moon would stop drifting away
- Earth’s day would match the lunar month
Tides would still exist—but they’d be almost frozen in place.
In practice, this will never happen.
Long before Earth could lock to the Moon, the Sun will interfere. As it brightens over the next billion years, Earth’s oceans are expected to evaporate. Without oceans, tides collapse. And a few billion years later, the Sun’s red giant phase will likely engulf Earth entirely.
The Earth–Moon dance has an ending—but not the one tidal locking predicts.
Why solar eclipses are slowly changing
There’s another, more poetic consequence of the Moon’s retreat.
Right now, the Moon appears almost exactly the same size in our sky as the Sun. That coincidence allows total solar eclipses, where the Sun is perfectly covered.
As the Moon moves farther away, it appears slightly smaller. Over hundreds of millions of years:
- Total eclipses will become rarer
- Annular eclipses (rings of sunlight) will dominate
- Eventually, total solar eclipses will vanish entirely
Future Earth—if it exists—will never experience the same celestial spectacle we enjoy today.
The science concepts behind the slow drift
A few key ideas help explain the Earth–Moon system:
- Tidal friction: Energy lost as tides rub against the seafloor, slowing Earth’s rotation
- Angular momentum: Conserved motion shared between Earth’s spin and the Moon’s orbit
- Tidal locking: A stable state where rotation and orbit synchronize
- Paleotides: Reconstructions of ancient tidal patterns from rocks and fossils
Together, they tell a story written not in years or centuries, but in deep time.
Why this matters now, even if it’s slow
The Moon drifting away won’t flood cities or end coastlines. But it reminds us of something essential: planetary change doesn’t need drama to be profound.
A shift of a few centimetres per year:
- Alters day length
- Softens tides
- Changes ecosystems
- Rewrites celestial events
Understanding these processes helps scientists model long-term Earth systems, from ocean circulation to coastal evolution. It also puts today’s rapid, human-driven changes into stark contrast with the slow, patient forces that normally shape planets.
The Moon doesn’t rush. It never has.
And yet, over billions of years, it has quietly transformed Earth—one millisecond, one tide, one centimetre at a time.
Key takeaways
| Change | What’s happening | Long-term effect |
|---|---|---|
| Lunar recession | Moon moves ~3.8 cm away each year | Weaker tides, longer days |
| Earth’s rotation | Slowing via tidal friction | Days gradually lengthen |
| Tidal energy | Slowly decreasing | Altered coastal and ocean dynamics |
| Eclipses | Moon appears smaller over time | Total eclipses eventually disappear |
