The young Earth once spun so rapidly that a day lasted just two to five hours. Scientists now believe that as our planet gradually slowed down and changed shape, it may have triggered powerful geological movements that helped shape Earth's earliest crust and lay the foundations for the continents we know today.
Around 4.5 billion years ago, Earth was a very different world. It was still young, extremely hot and spinning much faster than it does today. During this early period, a Mars-sized object collided with the newly formed planet. The enormous impact sent massive amounts of material into space, eventually creating the Moon.
However, this collision did more than create Earth's natural satellite. It also left our planet rotating at an extraordinary speed. Scientists estimate that a day on early Earth may have lasted only two to five hours.
Now, new research suggests that Earth's gradual slowdown may have played a much bigger role in shaping the planet than previously understood. According to Simon Lock, a researcher at the University of Bristol, changes in Earth's rotation and physical shape could have driven powerful geological activity during the planet's earliest history.
The findings, published in the Journal of Geophysical Research: Solid Earth, suggest that Earth's changing shape may have helped create the diverse rocks that eventually contributed to the formation of the continents.
How Earth's Rotation Changed Its Shape
Immediately after the giant impact that formed the Moon, Earth's rapid rotation caused it to become significantly flattened.
Instead of having the nearly spherical shape we see today, the young planet resembled a squashed ball. Its equatorial region bulged outward because of the powerful outward effect associated with its rapid spin.
In some extreme scientific models, Earth's width around the equator could have been almost twice its height from the North Pole to the South Pole.
Over millions of years, this unusual shape gradually changed.
The Moon's gravitational influence created tidal interactions between the two bodies. These interactions transferred rotational energy from Earth to the Moon, causing the Moon to move farther away while Earth's rotation gradually slowed.
As a result, Earth slowly became rounder.
Today, the planet completes one rotation in approximately 24 hours. However, the journey from its extremely fast early rotation to its modern spinning speed may have involved major changes to its surface and internal structure.
Earth's Changing Shape May Have Triggered Ancient Tectonic Activity
To understand what happened during this period, Simon Lock developed a new approach that combines calculations of Earth's changing shape and internal structure with models of the Moon's changing orbit.
He compared different scientific explanations of how the Moon formed, including scenarios in which Earth initially rotated much faster than previously assumed.
He then examined how the planet's surface might have responded as its shape gradually changed.
The results revealed an interesting possibility.
When Earth was spinning rapidly, the outward effect of rotation partly counteracted gravity near the equator. This may have allowed a thicker crust to develop around the equatorial region compared with the polar regions.
However, as Earth's rotation slowed and the planet became rounder, its surface experienced significant deformation.
The crust around the equator was compressed, while regions closer to the poles were stretched.
These movements could have generated enormous geological forces, potentially producing tectonic activity comparable to the movements occurring along modern plate boundaries.
In some of the faster-rotation scenarios, the compression around the equator may have reached rates comparable to the enormous geological forces involved in the formation of the Himalayas.
Even more remarkably, these forces could have extended around the entire equatorial region rather than being concentrated in one particular location.
According to the calculations, this period of intense geological deformation could have continued for tens of millions of years.
How These Movements May Have Helped Create Earth's First Continents
One of the biggest mysteries in Earth science is understanding how the planet developed such a wide variety of rocks so early in its history.
Most of Earth's original crust has disappeared. Billions of years of volcanic activity, erosion, melting and geological recycling have destroyed or transformed much of the evidence from that ancient period.
However, a few surviving rock fragments reveal that Earth's crust was already surprisingly diverse during its early history.
Scientists have traditionally explained this diversity through processes such as asteroid impacts, volcanic activity and the movement of material between Earth's surface and interior.
Lock's research introduces another possible explanation: Earth's changing shape.
As the crust was stretched and compressed, rocks exposed to water and weathering could have been pushed deeper underground. Under increasing temperatures and pressures, these materials could have melted and transformed into new types of rock.
This process may have helped produce silica-rich rocks similar to those that make up significant portions of Earth's modern continents.
In other words, the planet's changing rotation may have indirectly contributed to the development of the materials needed to build the first continents.
Changes Deep Inside Earth
The effects may not have been limited to the surface.
As Earth's crust experienced increasing pressure, some portions of the lower crust may have become sufficiently dense to sink into the underlying mantle.
This process could have created chemically different regions deep inside the planet.
Such regions may have influenced Earth's internal structure and helped explain why some ancient rocks have unusual chemical compositions.
The combination of surface deformation, rock recycling and changes within the mantle offers a possible explanation for the remarkable variety of geological materials found in Earth's earliest surviving rocks.
Although these processes still need further investigation, the research suggests that Earth's rotation deserves much greater attention when scientists study the planet's early evolution.
A New Way to Understand Earth's Ancient History
One major challenge for researchers is that almost no original crust from Earth's earliest period remains intact. Scientists therefore depend heavily on computer calculations, physical models and the limited geological evidence preserved in ancient rocks.
Lock's findings suggest that some existing models may be incomplete because they do not fully account for the effects of Earth's changing rotation and shape.
By including these factors, future studies could develop a more accurate picture of how the young planet evolved.
The research also highlights an important connection between Earth and the Moon. Their gravitational relationship may have influenced far more than ocean tides and the length of our days. It could also have helped determine how Earth's earliest surface developed.
Scientists still need to establish how strongly these proposed forces influenced actual geological processes. Nevertheless, the findings open an exciting new direction for understanding the planet's distant past.
Ultimately, the story of Earth's earliest continents may have begun with something surprisingly simple: a planet spinning incredibly fast and gradually slowing down. As Earth changed its shape, it may have triggered a geological transformation that helped create the world we live on today.
Reference: S. J. Lock, Tectonics on Early Earth Driven by Earth's Changing Shape During Tidal Recession of the Moon, Journal of Geophysical Research: Solid Earth (2026). DOI: 10.1029/2025jb033676
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