Earth may have had a ring 466 million years ago

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

A A study published this month The high number of impact craters during the Ordovician, the era before animals lived on Earth, is linked 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, producing dozens of meteorite-filled craters and deposits. Previous research has suggested that the event was the result of a meteorite impact. large asteroid which broke away from the main belt between Mars and Jupiter and sent rocky fragments into the inner solar system, where they struck our planet.

But what if this ancient body had been blown to smithereens on our doorstep? Researchers led by Andy Tomkins, a professor of earth and planetary sciences at Monash University in Australia, envision an asteroid passing thousands of miles from Earth, close enough to be torn apart by the planet’s gravity. The resulting debris then coalesced into a ring around the equator, a scenario that could be linked to dramatic changes in climate and biodiversity at the time.

“I got this idea when I read a popular science article about how Phobos and Deimos, the two moons orbiting Mars, were formed from remnants of rings around Mars,” said Dr. Tomkins, whose study is published in the journal Earth and Planetary Science Letters. “It got me thinking about what I would see in the geological record if Earth had once had a ring.”

Dr. Tomkins and his team mapped the locations of 21 Ordovician craters on Earth at that time. If the debris had come from the asteroid belt, the craters would have been distributed all over the planet. But the craters were clustered around the equator, suggesting that they were the result of meteorites falling from an equatorial ring.

“That’s what it revealed,” said Dr. Tomkins. “All of these planets are fairly close to the equator, and it’s very difficult for that to happen through natural impact cratering.”

The team claims that there is no evidence yet that Mars and the Moon experienced similar elevations in impact craters at this time, suggesting that the debris was localized to Earth. Additionally, the researchers point to Ordovician meteorites from Sweden that show low exposure to space radiation, meaning that the rocks fell to Earth within tens of thousands of years of their parent body breaking up. By contrast, debris from the asteroid belt typically is 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, triggering a major glaciation called the Hernandian Ice Age that shook life to its core. That connection is more speculative, but worthy of further study, Dr. Tompkins said.

“These multiple pieces of evidence come together to form what we think is a plausible hypothesis,” Dr. Tomkins said.

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

“The paper takes a completely new perspective, and this will definitely take us a step forward in understanding what happened in the Ordovician,” said Dr 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 “enticing” but remained unconvinced. She noted that meteorites could have struck regions far from the equator without leaving lasting geological traces. She was also skeptical about the proposed link between the ring and the Hernantian ice age.

“There are a lot of hypotheses here, which is not a bad thing,” Dr. Benedicks said of the study. “But I think there is physics and chemistry to be worked out.”

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

“What I particularly like is that the authors present a testable idea,” says Dr. Schmitz. “By looking for meteoric minerals in sediments from different latitudes, we will get an answer to whether the Earth really has a ring.”

Today, it is astonishing to imagine Earth in the past, almost entirely populated by marine life, surrounded by the remains of a broken space rock.