Earth probably had a Saturn-like ring system in the distant past

In a discovery that could reshape our understanding of Earth’s ancient history, researchers have found evidence suggesting that our planet may have once had a ring system around 466 million years ago. 

This ring system is believed to have formed at the onset of a period known as the Ordovician impact spike – a time of unusually intense meteorite bombardment.

Unusual positions of impact craters

The hypothesis emerged from reconstructions of plate tectonics from the Ordovician period, which reveal the unusual positions of 21 asteroid impact craters. 

What makes this finding puzzling is that all of these craters are located within 30 degrees of the equator, despite the fact that over 70 percent of Earth’s continental crust lay outside this region during that time. Conventional theories do not account for this anomaly.

Debris ring around Earth 

According to the researchers, this unusual impact pattern was caused by a large asteroid passing close to Earth. 

As the asteroid entered Earth’s Roche limit – the distance within which an object is pulled apart by tidal forces – it shattered, creating a debris ring around Earth. This is similar to the ring systems we see 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,” explained lead author Andy Tomkins from Monash University’s School of Earth, Atmosphere and Environment. 

“We also see that layers in sedimentary rocks from this period contain extraordinary amounts of meteorite debris.”

Climate implications of an Earth ring system

What makes this discovery even more intriguing are the potential climate implications. The researchers speculate that the ring could have cast a shadow over Earth, blocking sunlight and contributing to a significant global cooling event known as the “Hirnantian Icehouse.”

This cooling period, which occurred near the end of the Ordovician, is recognized as one of the coldest phases 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,” noted Tomkins.

Investigating the crater pattern 

Under normal circumstances, asteroid impacts on Earth are distributed randomly across the planet, just as we see with impact craters on the moon or Mars. 

However, to investigate whether the pattern of Ordovician craters was non-random and clustered closer to the equator, the researchers examined the continental surface area from that time capable of preserving such craters.

The experts focused on stable landmasses, or cratons, with rocks older than the mid-Ordovician period, avoiding areas buried under sediments or ice, regions that had been eroded, or those that had been affected by tectonic activity. 

Using Geographic Information System (GIS) analysis, the researchers identified suitable regions across various continents.

Regions well-suited for preserving craters

Regions like Western Australia, Africa, the North American Craton, and parts of Europe were found to be well-suited for preserving these craters. 

Surprisingly, while only 30 percent of this land area was located near the equator, all of the impact craters from this period were found within that narrow region. 

Statistically, the chances of this occurring by coincidence are incredibly slim – equivalent to flipping a three-sided coin and landing tails 21 times in a row.

Impact of asteroid debris rings 

This discovery has far-reaching implications beyond geology. It forces scientists to reconsider the broader impact that celestial events, like asteroid debris rings, might have had on Earth’s evolutionary history. 

The findings also raise new questions about the possibility of other ancient ring systems that may have influenced the development of life on our planet.

Could similar rings have existed during other periods of Earth’s history, affecting everything from the planet’s climate to the distribution of life? 

This research opens up a new frontier in studying Earth’s past, providing a fresh perspective on the dynamic interactions between our planet and the wider cosmos.

The study is published in the journal Earth and Planetary Science Letters.

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