Evidence from ancient impact craters suggests that Earth once had a ring similar to that of Saturn, causing significant climate disruptions on the planet’s surface.
Researchers from Monash University in Australia hypothesized that a rocky ring formed around Earth approximately 466 million years ago and existed for several tens of millions of years, as reported by New Atlas on September 16. This conclusion is based on several geological discoveries. During the period known as the Ordovician period, it appears that the number of impact craters on Earth increased.
Simulation of a ring potentially forming around Earth hundreds of millions of years ago. (Photo: IFL Science).
The research team mapped the locations of 21 known craters from that period, using tectonic plate motion models to track their positions at the time of impact. All craters appear to be situated within 30 degrees of the equator. Normally, one would expect them to be distributed randomly across the planet.
To determine whether this was a peculiar finding or a sampling error, the researchers calculated how much continental surface area from that time could retain craters for such long durations. They focused on the stable part of the crust that existed before the middle of the Ordovician period, excluding areas that were buried, eroded, or affected by tectonic activity. The best results were found in Western Australia, Africa, parts of North America, and Europe.
Subsequently, the team used the same type of tectonic modeling to trace back in time and discover where those areas were located on Earth during the Ordovician period. Only 30% of suitable land was near the equator. The fact that all 21 craters formed within this narrow band is statistically unusual, prompting them to wonder what caused the concentration of meteorite impacts around the equator. If Earth captured an asteroid passing by 466 million years ago, it could have caused the asteroid to break into many pieces and form a ring. Debris would have rained down on the planet, primarily at the equator, over several tens of millions of years.
The ring hypothesis may also explain several other mysteries from that period. Meteorite fragments in the craters show signs of not having traveled far in space before crashing to Earth, consistent with material from a relatively recent breakup of a large asteroid that created the ring.
About 20 million years later, Earth entered the Hirnantian glaciation, when temperatures dropped to the lowest levels in half a billion years. Due to Earth’s axial tilt with respect to the Sun, the equatorial ring cast shadows over parts of the planet’s surface, potentially causing a global cooling event.
This new hypothesis raises the possibility that rings are a phase that Earth and other planets experience multiple times in their lifetimes. Ultimately, the Saturn-like ring is estimated to have been around for 10 million years, suggesting that Earth was the pioneer in this case. Mars is currently also in the process of breaking apart one of its moons, which could create a new ring in about 20 to 40 million years. Next, the research team plans to model the process of asteroid breakup and ring formation, as well as how the ring evolves over time, followed by modeling the ring’s impact on climate. The findings are published in the journal Earth & Planetary Science Letters.
