When I was a wee lad with a growing interest in astronomy and science fiction, I sometimes wondered what it would have been like if Earth, like Saturn, had a ring.

As it turns out, not great, apparently.

In a paper published in Science Direct, Andrew Tomkins, Erin Martin and Peter Cawood suggest Earth may indeed have had a ring during the Ordovician, around 466 million years ago (Ma) with intriguing but catastrophic consequences.

As Tomkins explains in an article for The Conversation, the first clue for the team was an anomalous series of 21 impact craters from around that time, combined with ‘deposits of limestone across Europe, Russia and China containing very high levels of debris from a certain type of meteorite.’

The team then mapped where the craters would have been 466 Ma by using models of tectonic plate movement. Turns out they were all along the equator, with none near the poles.

As Tomkins writes, ‘… we measured how much of Earth’s land surface suitable for preserving a crater was near the equator at that time. Only about 30% of the suitable land was close to the equator, with 70% at higher latitudes.’

So, odds on something peculiar was going on.

The team speculates that Earth captured a passing asteroid which got close enough to exceed the Roche limit (where a smaller body’s internal gravity is overwhelmed by the tidal forces of a larger body). The broken remains of this asteroid then formed a ring around the Earth’s equator, and over time bits of it crashed into the Earth’s surface, forming the impact craters.

Finally, Tomkins et al speculated that the ring would have cast a shadow across large swathes of the Earth’s surface, which together with atmospheric dust from the impacts may explain the sudden plunge into what’s called the Hirnantian Ice Age about 445 Ma.

The team then further speculates that this rapid cooling would have forced animals to adapt to changing conditions, leading to the Great Ordovician Biodiversification Event. Uncomfortably abbreviated to GOBE, this was when Palaeozoic fauna replaced Cambrian fauna, leading to ‘… a spectacular increase in marine biodiversity at all taxonomic levels … ‘[i]

So  wearing a ring was not all bad news, I suppose.

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[i] Servais, Thomas, et al ‘The Great Ordovician Biodiversification Event (GOBE): The palaeoecological dimension’, ScienceDirect. See here.