Artistic impression by Oliver Hull

Researchers have found evidence suggesting that Earth may have had a ring system that formed 466 million years ago, a discovery that challenges the common understanding of our planet’s ancient history.

This surprising hypothesis, published last month in Earth and Planetary Science Letters, points to a period of unusually intense meteorite bombardment known as the Ordovician impact spike.

The research team studied plate tectonic reconstructions for the Ordovician period and noted where 21 asteroids hit on Earth. All these craters are located within 30 degrees of the equator—despite over 70% of Earth’s continental crust being outside these latitudes, an anomaly that conventional theories cannot explain.

They believe this localized impact pattern was produced after a large asteroid had a close encounter with Earth. As the asteroid got close enough (inside a distance called the Roche limit), it broke apart due to tidal forces, forming a debris ring around the planet—similar to the rings seen around Saturn and other gas giants today.

“Over millions of years, material from this ring gradually fell to Earth, creating the spike in meteorite impacts observed in the geological record,” said lead study author Professor Andy Tomkins, from Monash University in Australia. “We also see that layers in sedimentary rocks from this period contain extraordinary amounts of meteorite debris.”

“What makes this finding even more intriguing is the potential climate implications of such a ring system,” he said, speculating that the ring could have cast a shadow on Earth, blocking sunlight and contributing to a significant global cooling event known as the Hirnantian Icehouse.

This period, which occurred near the end of the Ordovician, is recognized as one of the coldest in the last 500 million years of Earth’s history.

“The idea that a ring system could have influenced global temperatures adds a new layer of complexity to our understanding of how extra-terrestrial events may have shaped Earth’s climate,” said Prof. Tomkins.

Normally, asteroids impact the Earth at random locations, so we see impact craters distributed evenly over the Moon and Mars, for example. To investigate whether the distribution of Ordovician impact craters is non-random and closer to the equator, the researchers calculated the continental surface area capable of preserving craters from that time.

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Craters on the moon

They focused on stable, undisturbed interiors of tectonic plates with rocks older than the mid Ordovician period, excluding areas buried under sediments or ice, eroded regions, and those affected by tectonic activity.

Using a GIS approach (Geographic Information System), they identified geologically suitable regions across different continents. Regions like Western Australia, Africa, North America, and small parts of Europe were considered well-suited for preserving such craters. Only 30 percent of the suitable land area was determined to have been close to the equator, yet all the impact craters from this period were found in this region.

The chances of this happening are tiny, because under normal circumstances, asteroids should hit Earth at all latitudes, at random, like we see on the surfaces of the Moon, Mars and Mercury.

“It’s extremely unlikely that all 21 craters from this period would form close to the equator if they were unrelated to one another,” said Tomkins. “We would expect to see many other craters at higher latitudes as well.”

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The implications of this discovery extend beyond geology, prompting scientists to reconsider the broader impact of celestial events on Earth’s evolutionary history. It also raises new questions about the potential for other ancient ring systems that could have influenced the development of life on Earth.

Could similar rings have existed at other points in our planet’s history, affecting everything from climate to the distribution of life? This research opens a new frontier in the study of Earth’s past, providing new insights into the dynamic interactions between our planet and the wider cosmos.

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