Earth may have had a ring during the middle Ordovician, from ca. 466 Ma, breakup of an asteroid passing within Earth’s Roche limit likely formed the ring.

Among several features preserved is a near-equatorial band of impact craters. Shading of Earth by the ring may have triggered a global icehouse period. The sientists suggested in the report ‘Evidence suggesting that earth had a ring in the Ordovician‘ that a large L chondrite asteroid had a near miss encounter with Earth at ca. 466 Ma, which caused it to break up as it passed through Earth’s Roche limit. This can explain why sedimentary rocks from this time contain 99 % L chondrite material at abundances 2–3 orders of magnitude above background, with extremely brief Cosmic-ray Exposure Ages of Meteorites (CRE ages). They have further suggested that the resulting fragments formed a debris ring that decayed over several tens of millions of years resulting in an anomalous spike in impact cratering rate. This hypothesis may explain why all impact structures from this time are located proximal to the equator; impacts from bodies originating in the asteroid belt are expected to be randomly distributed across the globe. We have estimated the probability that this impact structure distribution resulted from random unrelated impactors at 1 in 25 million. They speculate that this ring may have promoted the coldest global cooling event in the last 540 million years, the Hirnantian Icehouse period.

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