Earth may have had a ring 466 million years ago

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Some scientists say that if we looked from Earth 466 million years ago, we might have seen a bright ring stretching across the sky.

A A study published this month He links the increase in impact craters during the Ordovician period, the period before animals appeared on Earth, to a ring of asteroid debris that surrounded our planet for millions of years.

Scientists have long speculated about the origin of the Ordovician meteorite event, when Earth was bombarded by space rocks at an unusually high rate, creating dozens of meteorite-filled craters and deposits. Previous research involved to a large asteroid which exploded in the main belt between Mars and Jupiter and sent rocky fragments into the inner solar system, where they littered our planet.

But what if this ancient body had been blown to smithereens on our doorstep? A team of researchers led by Andy Tomkins, a professor of Earth and planetary sciences at Monash University in Australia, imagines an asteroid passing thousands of kilometres from Earth, close enough to be torn apart by the planet’s gravity. The fragments of the breakup would have come together to form a ring around the equator, a scenario that could be linked to dramatic changes in climate and biodiversity at the time.

“I got the idea when I read a popular science article that Phobos and Deimos, the two moons that surround Mars, formed from the remains of a ring around Mars,” said Tompkins, whose study is published in the journal Earth and Planetary Science Letters. “That got me thinking about what it would look like, in the geological record, if Earth had a ring in the past, too.”

Tompkins and his team mapped the locations on Earth where 21 Ordovician craters could have been found at the time. If the remains came from the asteroid belt, the craters should be distributed all over the planet. But the craters were clustered around the equator, suggesting that they were formed by meteorites that fell from the equatorial ring.

“That’s what exposed them,” Tompkins said. “They’re all very close to the equator, and it’s very difficult for that to happen with normal impact drilling.”

The team argues that, to date, there is no evidence that Mars and the Moon experienced similar peaks of impact craters around that time, suggesting that the location of the debris was limited to Earth. Additionally, the researchers point to Ordovician meteorites from Sweden that show low exposure to radiation from space, meaning that the rocks fell to Earth tens of thousands of years after their parent body broke up. In contrast, debris from the asteroid belt typically has been exposed to space radiation for millions of years.

The team also wondered whether the shadow cast by the ring on Earth might have cooled the planet, which would have led to a major ice age called the Hernanthian glaciation that shook the course of life. That connection was more speculative, but worthy of further study, Tompkins said.

These “multiple pieces of evidence” are being combined into what “we believe is a plausible hypothesis,” Tomkins said.

Birger Schmitz, a professor of geology at Lund University in Sweden, praised the team’s new and creative approach, but said more data was needed.

“The paper takes a completely new perspective, which will definitely allow us to take a step forward in understanding what happened in the Ordovician,” said Schmitz, who is also affiliated with the Purple Mountain Observatory in China.

Gretchen Benedix, a professor of earth and planetary sciences at Curtin University in Australia, called the study “provocative” but was unconvinced. She noted that it was possible for meteorites to have struck far from the equator without leaving geological traces. She was also skeptical about the proposed connection between the ring and the Hernantian glaciation.

“There’s a lot of hypothetical data in all of this, which is not a bad thing,” Benedicks said of the study. “But I think there’s physics and chemistry to work out.”

To this end, Tomkins and his colleagues have identified ways to test their hypothesis, including studies of Ordovician meteorites at different latitudes and more complex models of how a decaying asteroid formed Earth’s ring.

“What I like most is that the authors present an idea that can be tested,” Schmitz said. “By looking for meteorite minerals in sediments from different latitudes, we will get an answer to whether Earth really has a ring.”

At the moment, it’s exciting to imagine a past Earth, almost entirely populated by marine life, surrounded by the fragmented remains of a space rock.