Earth is slowing down, but don’t worry about adjusting your calendar anytime soon. Earth’s rotation is slowing by about 1.7 milliseconds per century, which means a 25-hour day won’t happen for roughly 200 million years. This process is so slow that you won’t notice any difference in your lifetime or even in thousands of human lifetimes.
The idea might sound strange, but it’s based on solid science. The Moon’s gravitational pull creates friction with Earth’s oceans, gradually slowing our planet’s spin. At the same time, changes inside Earth’s core and shifts in ice and water also play a role in this process.
You might wonder how scientists know this is happening and what it means for life on Earth. The answer involves precise measurements, ancient geological records, and an understanding of the forces that have shaped our planet for billions of years. Days were once much shorter—during the dinosaur era, a day lasted only about 23 hours, and 1.4 billion years ago, days were just 18 hours and 41 minutes long.
Why Earth’s Days Are Getting Longer
Earth’s rotation determines how long a day lasts, and this spin is gradually slowing down due to gravitational forces from the Moon. The main cause is tidal friction, which transfers Earth’s rotational energy to the Moon over millions of years.
Earth’s Rotation and Day Length
A single rotation of Earth on its axis takes 24 hours, which gives you the length of a standard day. This rotation speed isn’t constant though. When Earth first formed about 4.5 billion years ago, it spun much faster than it does today.
During the age of dinosaurs, a day lasted only about 23 hours. As Earth’s spin continues to slow, the length of day increases by tiny amounts. Currently, days are lengthening by 1.7 milliseconds per century.
You won’t notice these changes in your lifetime because they happen so slowly. The changes add up over geological timescales.
The Moon’s Effect: Tidal Braking
The Moon’s gravitational pull creates ocean tides on Earth, which causes a process called tidal braking. This process slows Earth’s rotation while simultaneously pushing the Moon into a slightly higher orbit.
Tidal braking increases the length of your day by 2.3 milliseconds per century. As the Moon pulls on Earth’s oceans, it creates a bulge of water. Earth rotates faster than the Moon orbits, so this bulge moves ahead of the Moon’s position.
The Moon’s gravity pulls back on this bulge, which acts like a brake on Earth spin. This transfers Earth’s rotational energy to the Moon, causing it to drift farther away at about 1.5 inches per year.
The Role of Tidal Friction
Tidal friction occurs when the Moon’s gravitational force pulls on Earth’s oceans and creates resistance against the planet’s rotation. The ocean water doesn’t respond instantly to the Moon’s pull, creating a slight lag.
This lag means the tidal bulge sits at an angle rather than directly under the Moon. The friction between moving water and the ocean floor, plus the friction within Earth itself, converts rotational energy into heat. In about 200 million years, this process will result in 25-hour days as the Moon moves farther away and Earth continues slowing.
The energy lost through tidal friction gradually decreases Earth’s rotation speed. This same mechanism affects the Moon, which is why one side always faces Earth.
The Path to a 25-Hour Day: Scientific Predictions
Earth’s rotation is slowing at a rate of 1.7 milliseconds per century, and scientists predict days will stretch to 25 hours in approximately 200 million years.
Timetable for Earth’s Slowdown
Scientists have calculated that Earth will have 25-hour days in about 200 million years based on current rotation rates. This timeline represents an incredibly distant future with no practical impact on your life or even human civilization as we know it.
The Moon moves away from Earth at 3.82 centimeters annually. Over the span of 200 million years, this gradual drift will accumulate enough to add that extra hour to your day.
Some scientific models estimate this could occur within 200 to 225 million years. The variation in predictions depends on factors like changes in Earth’s core and how tidal forces evolve over time.
Milliseconds Per Century: Measuring the Change
Your days are getting longer by 1.7 milliseconds per century due to lunar tides. This measurement is so small you’ll never notice it in your lifetime.
The change happens because tidal forces created by the Moon’s gravity gradually transfer energy from Earth’s rotation to the Moon’s orbit. As the Moon gains this energy, it moves farther away and Earth’s spin slows down.
Scientists measure these tiny changes by studying ancient rock formations and comparing them to modern astronomical data. This precision allows researchers to track how the length of a day has changed over billions of years.
Historical and Future Projections
During the age of dinosaurs, your day would have lasted only 23 hours. Going back 1.4 billion years, a day was just 18 hours and 41 minutes.
Researchers at the University of Wisconsin-Madison examined rock formations from 90 million years ago to understand how Earth’s rotation has changed. They discovered that the Moon’s recession rate has varied throughout geological time due to continental drift and changes in Earth’s rotation speed.
Historical progression of day length:
- 1.4 billion years ago: 18 hours 41 minutes
- 90 million years ago: ~23 hours
- Today: 24 hours
- 200 million years from now: 25 hours
The rate of change isn’t perfectly constant. Your planet’s internal dynamics and how continents shift across the surface affect how quickly the slowdown occurs.
Forces Driving Earth’s Rotational Changes
Several powerful forces work together to alter how fast Earth spins on its axis. The Moon’s gravitational pull creates the strongest long-term effect, while climate change is causing mass redistribution that adds to the slowdown, and movements deep inside our planet also play a role.
Gravitational Interaction with the Moon
The Moon pulls on Earth’s oceans through gravity, creating tidal friction that acts like a brake on our planet’s rotation. This process, called tidal braking, is increasing the length of your day by 2.3 milliseconds per century. As Earth loses rotational energy, the Moon uses that energy to move into a slightly higher orbit.
The Moon gradually drifts about 1.5 inches away from Earth each year. This means the tidal effect will continue to slow Earth’s rotation for hundreds of millions of years. Days were just 18 hours long 1.4 billion years ago, and 70 million years ago during the age of dinosaurs, your day would have been only 23 hours.
Melting Ice and Mass Redistribution
The melting of ice caps in Greenland and Antarctica is causing water to flow from the poles toward the equator. This shift in mass affects Earth rotation like a figure skater extending their arms during a spin. When mass moves away from the rotation axis, the planet slows down.
Global warming is pushing more water into equatorial oceans, which creates a drag effect on Earth’s spin speed. This could have a more significant impact than the Moon’s natural tidal friction. The change might seem tiny now, but it affects global timekeeping systems and GPS satellites that depend on precise measurements of Earth’s rotation.
Influence of Earth’s Core and Crust
Deep inside Earth, movements in the liquid iron outer core and the solid inner core also affect rotation speed. Earth’s inner core has been slowing down since 2010, which contributes to changes in day length. The churning liquid iron creates gravitational forces that interact with the mantle above.
These internal dynamics work together with surface changes to alter both the speed of rotation and the position of Earth’s axis. Your planet’s axis shifts about 30 feet every hundred years due to these combined forces.
Climate Change and Its Accelerating Impact
Climate change is reshaping Earth’s physical properties in ways that extend beyond temperature increases. The redistribution of water from melting ice sheets adds mass to the oceans, which affects how our planet rotates on its axis.
Polar Ice Melt and Sea Level Rise
The polar ice melt and freshwater injection into the North Atlantic Ocean now exceed prior estimates. Greenland and Antarctica are losing ice at accelerating rates as global temperatures continue to climb.
Sea levels are rising faster than scientists previously predicted. The water from melting ice doesn’t just add volume to the oceans. It relocates mass from the poles toward the equator.
This movement happens because ice that was once locked on land now flows into the seas. Climate change is accelerating according to recent reports from leading climate scientists. The warming rate has increased by more than 50% since 2010 compared to the 1970-2010 period.
Redistribution of Mass and Spin Rate
When massive amounts of water shift from polar ice sheets to the oceans, you’re witnessing a fundamental change in how Earth’s mass is distributed. This redistribution affects the planet’s rotation speed through the same physics that governs a spinning figure skater.
Benedikt Soja from ETH Zurich studies how climate-driven changes impact Earth’s rotation. His research shows that melting ice contributes to the lengthening of our days. The effect is small but measurable with modern instruments.
The process works like this:
- Ice melts at the poles
- Water flows toward the equator
- Mass moves away from Earth’s axis
- Rotation slows down slightly
Climate Models and Future Scenarios
Scientists now warn that by early 2028 society will have emitted enough greenhouse gases to lock Earth into hitting the 1.5°C warming limit. Research published in the Proceedings of the National Academy of Sciences and other journals tracks these changes with increasing precision.
Current models predict continued acceleration of global warming over the coming decades. The top ten hottest years on record have all occurred within the last decade. This means the effects on Earth’s rotation will likely intensify as more ice melts and sea levels continue rising.
How Scientists Measure the Changing Length of Earth’s Day
Scientists use atomic clocks and satellite technology to track tiny changes in how fast Earth spins. Organizations like the International Earth Rotation and Reference Systems Service monitor these measurements and compare them to historical records.
Role of Atomic Clocks
Atomic clocks let scientists measure time with extreme accuracy. These devices can detect changes as small as milliseconds or even microseconds in the length of your day.
Atomic clocks and satellite laser ranging have revealed that the length of day changes over periods ranging from a few weeks to several years. The measurements show variations so precise that scientists recorded the shortest day in history on June 29, 2022, when Earth completed its rotation 1.59 milliseconds faster than the standard 24 hours.
Scientists can now measure the length of day to high accuracy over integration times of only a few hours. This level of precision allows researchers to track not just long-term trends but also short-term fluctuations caused by atmospheric changes, ocean currents, and other factors.
International Timekeeping Organizations
The International Earth Rotation and Reference Systems Service (IERS) monitors all changes in Earth’s rotation. This organization tracks your planet’s spin and provides data to scientists worldwide.
IERS uses a global network of observation stations that employ different measurement techniques. These include very-long-baseline interferometry, which uses radio telescopes to track distant quasars as reference points. When Earth’s rotation speed changes, the apparent position of these cosmic objects shifts slightly.
The organization maintains International Atomic Time (TAI), which serves as the basis for coordinated universal time. When Earth’s rotation slows down or speeds up significantly, IERS sometimes adds or subtracts leap seconds to keep clock time aligned with Earth’s actual rotation.
Historic Data and Modern Monitoring
Scientists compare modern atomic clock measurements against historical astronomical records to understand long-term trends. Over millions of years, Earth’s rotation has been slowing down due to friction from tides driven by the Moon, adding about 2.3 milliseconds to each day per century.
Recent data shows unexpected patterns. After years of speeding up, Earth began slowing down again in 2023, marking the first time in seven years that the average day length increased. Scientists can now track 10-day fluctuations of about 0.1 milliseconds and identify annual variations with amplitudes of 0.34 milliseconds.
Implications for Timekeeping and Society
Changes in Earth’s rotation speed create measurable challenges for global timekeeping systems. Even small variations of milliseconds can affect digital infrastructure, GPS accuracy, and space missions that rely on precise time measurements.
Leap Seconds and Negative Leap Seconds
Your digital devices depend on atomic clocks that keep perfect time, but Earth doesn’t rotate at a constant speed. When our planet’s rotation slows down, timekeepers add a leap second to keep atomic time aligned with Earth’s actual rotation. These adjustments have been added 27 times since 1972 to account for the gradual slowing caused by the moon’s gravitational pull.
However, you might see something unprecedented soon. Climate change is causing Earth to spin more slowly, but the planet’s liquid core is also changing how fast the surface spins. When Earth rotates faster than expected, timekeepers may need to subtract time instead of adding it.
The last leap second was added in 2016. Only four have been added in the past 23 years, showing the complexity of how climate change impacts day length.
Impact on Technology and Global Infrastructure
Your GPS navigation, financial transactions, and internet communications all depend on split-second timing accuracy. A few milliseconds added to the 24-hour period could cause problems for your digital infrastructure and the accuracy of GPS satellites orbiting the planet.
Computer systems worldwide are synchronized to Coordinated Universal Time (UTC). When leap seconds occur, your devices must adjust instantly. This creates potential glitches in:
- Stock trading systems that process millions of transactions per second
- Telecommunications networks that route calls and data
- Power grids that balance electricity distribution
- Navigation systems used in aviation and shipping
The variations in rotation speed mean your technology must constantly adapt to keep accurate time measurements.
Potential Effects on Space Travel
Your space missions require extremely precise timing for navigation and communication. The changing rotation speed could have consequences for space travel, as satellites and spacecraft calculate their positions based on Earth’s rotation.
Spacecraft trajectory calculations depend on knowing exactly where Earth will be at any given moment. When the planet’s rotation varies by milliseconds, these calculations become more complex. Your mission control teams must account for these variations when launching rockets or communicating with distant probes.
The slowing rotation affects how space agencies plan missions decades in advance.
Frequently Asked Questions
The slowing of Earth’s rotation raises important questions about how we track time, what causes these changes, and what effects they have on our planet. Scientists use precise measurements to understand these shifts while considering both natural forces and human impacts.
How does the gradual slowing of Earth’s rotation impact our timekeeping systems?
Our timekeeping systems rely on Coordinated Universal Time, which must stay in sync with Earth’s actual rotation. When Earth’s rotation changes, scientists add or remove leap seconds to keep digital time accurate.
GPS satellites and other technology need to account for these tiny changes. If they don’t adjust for Earth’s changing speed, their positioning data becomes unreliable. A difference of just a few milliseconds can add up over time and cause problems for systems that depend on exact timing.
The International Earth Rotation and Reference Systems Service added the last leap second on December 31, 2016. They monitor Earth’s rotation constantly to decide when adjustments are needed.
What mechanisms contribute to the lengthening of Earth’s days over time?
The Moon pulls on Earth through gravitational forces, which acts like a brake on our planet’s spin. This happens because the Moon is gradually pulling away from Earth, taking rotational energy from our planet as it moves into a higher orbit.
Tidal forces from the Moon are the main cause of this long-term slowdown. The Moon’s gravity creates bulges in Earth’s oceans, and the friction from these moving tides gradually slows our planet’s rotation.
Solar atmospheric tides also play a role in Earth’s rotation speed. Research shows that about 1 to 2 billion years ago, solar tides were strong enough to stall the length of a day at 19 hours for around a billion years.
In what way do changes in Earth’s rotation affect the natural environment and ecosystems?
Changes in day length affect climate patterns across the planet. The amount of sunlight different areas receive shifts as days get longer, which can alter temperature patterns and weather systems.
Ocean currents respond to changes in Earth’s rotation speed. These currents help distribute heat around the globe and influence marine ecosystems.
The evolution of life on Earth has been shaped by changing day lengths. When the length of a day stalled at 19 hours about 1 to 2 billion years ago, the biggest surges in oxygen levels on Earth occurred. This suggests that stable day lengths may have helped certain life forms thrive and produce more oxygen.
What methods do scientists use to measure the rate at which Earth’s rotation is slowing?
Atomic clocks provide the most accurate measurements of Earth’s rotation. These clocks can detect changes as small as milliseconds in the length of a day.
Scientists also study the fossil record to understand historical day lengths. By examining growth patterns in ancient corals and sedimentary rocks, they can determine how long days were millions of years ago. About 620 million years ago, a day was only 21.9 hours long, and there were over 400 days in a year.
The International Earth Rotation and Reference Systems Service tracks Earth’s rotation continuously. They collect data from stations around the world and predict future changes in day length.
How will the extension of Earth’s day length over millions of years influence future human activity?
Future timekeeping systems will need to adapt to longer days. Your calendars and clocks will require adjustments to stay aligned with Earth’s actual rotation.
In about 200 million years, a day will last 25 hours instead of 24. This change will affect how future civilizations structure their daily schedules and work patterns.
Energy systems and infrastructure will need modifications. Solar panels and other technologies that depend on day-night cycles will require different designs to work efficiently with longer days.
Can human-induced changes to the planet have any significant effect on the rate of Earth’s rotational slowing?
Climate change may influence Earth’s rotation speed in the short term. The melting of ice caps could be slowing the rate of Earth’s rotation by redistributing mass on the planet’s surface.
When ice melts and moves from the poles toward the equator, it changes how mass is distributed on Earth. This redistribution can affect rotation speed, similar to how a figure skater spins slower when they extend their arms.
However, these human-induced effects are small compared to the natural forces that control Earth’s long-term rotation. The Moon’s gravitational pull remains the dominant factor in slowing Earth’s spin over millions of years.
Human activities can cause measurable short-term changes in rotation speed. But these effects won’t significantly alter the long-term trend of Earth moving toward 25-hour days.
