Earth’s Rotation Changes: New Insights from Recent Research

April 20, 2025

Recent scientific studies have revealed fascinating insights into subtle changes in Earth’s rotation, driven by both natural and human-induced factors. These findings, grounded in rigorous research, shed light on why the planet’s spin is experiencing measurable shifts, impacting everything from the length of a day to the stability of satellite orbits.

Human Activities Slow Earth’s Spin

One of the most striking discoveries comes from NASA’s research on China’s Three Gorges Dam, the world’s largest hydroelectric power station. The dam’s massive reservoir, holding 40 billion cubic meters of water, has slightly altered Earth’s rotation by redistributing mass across the planet’s surface. This shift in mass increases the planet’s moment of inertia, slowing its spin by approximately 0.06 microseconds per day. While this change is minuscule, it is measurable and highlights the profound impact of human engineering on planetary dynamics. The redistribution of water mass, particularly toward the equator, acts like a figure skater extending their arms to slow their spin.

Similarly, excessive groundwater pumping has been identified as a significant contributor to changes in Earth’s rotation. A study by researchers in South Korea found that the extraction of 2,150 gigatons of groundwater between 1993 and 2010 has tilted Earth’s axis by approximately 31.5 inches (80 centimeters). This redistribution of water, primarily for agriculture and urban use, mimics the effect of melting ice sheets, shifting mass toward the equator and slowing the planet’s rotation. This tilt is equivalent to about 0.24 inches of sea-level rise, demonstrating the interconnectedness of human activities, climate change, and Earth’s rotational dynamics.

Earth’s Inner Core: A Dynamic Influence

Beyond human influences, changes deep within the Earth are also affecting its rotation. A groundbreaking study published in Nature Geoscience in February 2025 revealed that Earth’s inner core, a solid metal sphere 3,200 miles beneath the surface, is not only slowing its rotation but also changing shape. By analyzing seismic waves from 168 paired earthquakes near the South Sandwich Islands, researchers found evidence of structural changes in the core’s outermost layer. These changes, detected through subtle differences in wave patterns, suggest that the core’s surface is dynamic and deformable, potentially altering the planet’s rotation and the length of a day by milliseconds over long timescales.

The inner core’s rotation has been a subject of debate since the 1990s. Recent data indicates that it spun faster than the rest of the planet until around 2010, when it began to slow, possibly even reversing relative to the surface. This slowdown, combined with structural changes, challenges previous assumptions about the core’s stability and underscores the complex interplay between Earth’s internal layers.

Natural Forces and Cosmic Interactions

Earth’s rotation is also influenced by natural forces, particularly the Moon’s gravitational pull. Over billions of years, the Moon has gradually slowed Earth’s spin, lengthening days from a mere 10 hours in the planet’s early history to the current 24-hour cycle. This deceleration, caused by tidal friction, continues to extend day length by milliseconds over eons. The Moon’s slow drift away from Earth further weakens its gravitational influence, affecting ocean tides, atmospheric patterns, and Earth’s axial tilt, which can drive long-term climate changes.

Additionally, historical data from lunar eclipses and occultations dating back to 720 BCE have provided insights into Earth’s rotational fluctuations. Research from ETH Zürich, published in December 2024, links subtle shifts in the molten iron outer core to variations in day length, confirming the core’s role in these dynamics.

Implications and Future Research

While these changes to Earth’s rotation are subtle on human timescales, they have significant implications for scientific measurements and long-term environmental processes. The slight increase in day length affects the stability of satellite orbits, requiring adjustments for precise astrophysical calculations. Furthermore, the redistribution of mass from groundwater pumping and large-scale infrastructure contributes to sea-level rise, with regional variations that could impact coastal ecosystems and communities.

The discovery of the inner core’s dynamic behavior opens new avenues for geophysical research. Scientists emphasize the need for better models to understand how these internal changes interact with external forces like climate change and human activities. As John E. Vidale, a researcher involved in the inner core study, noted, “What we ended up discovering is evidence that the near surface of Earth’s inner core undergoes structural change,” signaling a need for further exploration of Earth’s hidden depths.

A Planet in Motion

From massive dams to groundwater extraction and the restless inner core, Earth’s rotation is influenced by a delicate balance of human, geological, and cosmic forces. These findings, reported in reputable sources like Nature Geoscience and NASA studies, underscore the interconnectedness of Earth’s systems and humanity’s growing influence on them. As research continues, scientists aim to unravel the full extent of these changes and their implications for our planet’s future.

For more information on these discoveries, explore the latest research at Nature or NASA.