Scientists confirm: The 24-hour day may not last much longer.

Clocks feel solid and familiar, yet deep beneath that ticking order, our planet quietly rewrites the rules of time.

For generations, we treated 24-hour days as a natural constant, like gravity or sunrise. New research now suggests that this comfort is misleading, and that our idea of what “a day” means has already started to slip.

Scientists say the 24-hour day is not eternal

Researchers at the Technical University of Munich have joined a growing chorus of scientists who argue that the 24-hour day will not last forever. Their work looks at tiny changes in the way Earth spins on its axis and shows that our planet does not keep perfect time.

Most people only notice time shifts when we change the clocks for daylight saving time. We lose or gain an hour of sleep and complain for a week. That shuffle, though, is purely human. The Munich team focused on something deeper: Earth’s rotation, and how it drifts over millions of years.

The length of a day is not fixed in stone. Earth’s rotation speeds up and slows down, stretching and squeezing the time between two sunrises.

Their conclusion sounds simple and a bit unsettling: Earth is gradually slowing down. As the planet rotates more slowly, the length of a day increases. Not enough for us to notice at breakfast, but clearly enough when you look across geologic time.

Why days change length over deep time

Several forces tug at our planet and alter its spin. None of them act quickly, but together they reshape the clock over hundreds of millions of years.

The main culprits behind Earth’s slowing spin

• Lunar tides: The Moon pulls on Earth’s oceans, creating tides that drag against the seafloor and bleed away rotational energy.
• Solar influence: The Sun also raises tides in the oceans and atmosphere, adding its own gentle braking effect.
• Internal structure: Changes in Earth’s core, mantle, and crust shift how mass is distributed, which can alter rotation speed.
• Ice and water redistribution: Melting ice caps, rising seas, and changing groundwater move huge amounts of mass across the surface.
• Major geologic events: Mountain building, supervolcanoes, and continental drift subtly reshape the planet’s spin over vast timescales.

We already see short-term effects. Powerful earthquakes shift mass just enough to change the length of the day by a fraction of a millisecond. That sounds tiny, yet atomic clocks can detect it.

Over billions of years, these small nudges add up, turning a barely measurable delay into an extra hour in the day.

From 10 hours to almost 24: Earth’s ancient days

The Munich study echoes previous research that looked back in time using geologic records, fossils, and ancient coral growth rings. These natural archives act like time-lapse cameras.

Evidence suggests that between around 2 billion and 600 million years ago, Earth’s day lengthened from about 10 hours to roughly 19.5 hours. Life evolved under a dramatically different rhythm, with more frequent sunrises and sunsets.

That history shows one clear pattern: Earth’s rotation keeps slowing. The change is not linear, and many processes interact, but the overall trend points in one direction.

What a 25-hour day could look like

The headline finding that catches attention is this: if current trends continue, future days could stretch to 25 hours. According to estimates cited by the Munich team, this shift would take roughly 200 million years.

To put that in perspective, 200 million years is about as long as the time between the first dinosaurs and us. Humanity will likely look nothing like it does today, assuming it even still exists as we know it.

The 25-hour day will not affect your alarm clock, or your children’s, or even the clocks of any civilization remotely like ours. This is a story written on geologic, not human, timescales.

Still, the idea invites a question: if some intelligent descendants of ours live through that change, how would their world feel?

Calendars, clocks, and a different daily rhythm

If a day lasts 25 hours, the total length of the year (one full orbit around the Sun) would remain almost the same. The planet’s path around the Sun barely depends on its spin. What changes is how many times Earth rotates during that orbit.

That means future societies would face a choice: adapt clocks and calendars to match the new rotation, or keep a legacy 24-hour system and watch it drift relative to sunrise.

Parameter	Today	In ~200 million years (estimate)
Length of one day	24 hours	25 hours
Days per (same) year	≈365.24 days	≈350–360 longer days
Human timekeeping	24-hour clock	Likely redefined to match longer days

A small change in day length would reshape daily life. Work schedules, school timetables, and shift patterns would adjust. Night shifts could last longer. People might split their waking hours differently between morning and evening.

Biology under a longer day

One of the most sensitive systems affected by day length is biology. Humans, animals, and even plants align their internal clocks with the cycle of light and dark.

Circadian rhythms under pressure

Our bodies rely on circadian rhythms-roughly 24-hour cycles that govern sleep, hormone release, digestion, and mood. These rhythms sync with daylight but also depend on genes and brain structures that evolved under a specific day length.

A 25-hour natural day would push living organisms to retune their internal clocks, potentially changing when they sleep, eat, and reproduce.

We already see how fragile this balance can be. Jet lag, night shifts, and late-night screen time disrupt circadian timing and are linked to health problems such as metabolic disorders, depression, and cardiovascular disease.

Given enough generations, evolution would likely favor organisms better suited to the new rhythm. Future humans, if they exist, might not struggle with a 25-hour day the way we struggle with a red-eye flight.

Plants, animals, and the shape of ecosystems

The shift would not stop at humans. Plants time their photosynthesis, flowering, and seed release with day–night cycles. Many animals hunt, migrate, and reproduce on precise schedules tied to light, tides, or lunar phases.

Longer days could alter:

• How long plants can photosynthesize each day, which might change growth patterns and yields.
• The timing of insect activity, including pollinators and disease-carrying species.
• Predator–prey cycles, if hunting and resting periods shift.
• Marine life behavior linked to tides, which depend on both rotation and the Moon’s pull.

None of these changes would be abrupt. Evolution would respond gradually as the day stretches. Ecosystems would adjust, collapse, or reform, the way they have throughout Earth’s history.

What this means for how we think about time now

Even though the 25-hour day lies far beyond any realistic human horizon, the research matters for today’s science. It shapes how we build long-term climate models, interpret ancient rocks and fossils, and maintain ultra-precise timekeeping.

Modern navigation, satellite systems, and financial networks all rely on atomic clocks synchronized with Earth’s rotation. As our planet slows, agencies already insert “leap seconds” from time to time to keep official time close to Earth’s actual position relative to the Sun.

The slow drift in Earth’s spin forces us to stitch together two concepts of time: the perfect tick of atomic clocks and the messy, changing rhythm of a real planet.

Geophysicists also use subtle variations in day length to peer into Earth’s interior. Tiny irregularities can hint at flows in the liquid outer core, shifts in the mantle, and even long-term climate patterns as ice and water move across the globe.

A thought experiment: living on a 25-hour Earth

Imagine a distant descendant of humanity trying to design a daily routine under a 25-hour sky. They might keep something like our familiar pattern but stretched: perhaps 17 waking hours and 8 hours of sleep, or a split day with two shorter rest periods.

City planners could time public transportation, energy use, and lighting to match a longer active phase. Power grids might need new strategies if more daylight shifts when people work and when they rest. At higher latitudes, where daylight already swings wildly between seasons, the experience of long summer days and dark winters would gain another layer of complexity.

For anyone who already feels that 24 hours never seem like enough, the idea of an extra hour sounds tempting. Yet daily pressure usually comes from social and economic demands, not planetary physics. A longer day would quickly fill with new obligations, new expectations, and new forms of fatigue.

Beyond the 24-hour mindset

The research from Munich and other teams nudges us to see time not as a rigid frame but as an evolving part of a living planet. Days once passed in ten swift hours when early life clung to the oceans. They stretched through deep time as tides and tectonic plates quietly altered Earth’s spin.

When scientists talk about a 25-hour day in 200 million years, they are not predicting tomorrow’s chaos. They are tracing a slow story that links astronomy, geology, biology, and technology. That story reminds us that even concepts as familiar as “a day” can shift beneath our feet.