...
By Jess Thomson
Science Reporter
0
Share
Newsweek is a Trust Project member
See more of our trusted coverage when you search.Prefer Newsweek on Googleto see more of our trusted coverage when you search.
Back when the Earth was crawling with trilobites and other strange shelled creatures, our planet may have had a ring just like Saturn's.
This ancient ring system is thought to have formed about 466 million years ago, at the beginning of a period when Earth was regularly hit by meteorites, according to a new paper in the journal Earth and Planetary Science Letters.
This era of intense bombardment, known as the Ordovician impact spike, may have resulted from meteorites falling from the ring rather than flying in from space, which would explain the strange placement of craters.
Read More on Science
...
The researchers' idea that Earth once had rings comes from reconstructions of Earth's plate tectonics from the Ordovician period—which ran between 485.4 million years and 443.8 million years ago—including the positions of 21 impact craters from the Ordovician impact spike.
The Ordovician impact spike was previously thought to have been caused by the breakup of a large asteroid in the belt between Mars and Jupiter. However, all 21 of the craters are located within 30 degrees of the equator, leaving 70 percent of the Earth's surface more or less untouched. This is incredibly unlikely to occur by chance, but previous theories cannot explain why this may have happened.
The researchers suggest that this unlikely pattern of impacts could be explained by an asteroid having broken apart after a close call with the Earth and the remains forming a ring around the planet, from which the meteorites fell to the ground and created the craters.
"The hypothesis is that a large asteroid broke up when it had a close encounter with the Earth 466 million years ago. Debris may have formed a ring around the Earth, and from there rained down on the Earth to produce the geological features we can see today," study lead author Andy Tomkins, a professor at Monash University's School of Earth, Atmosphere and Environment in Australia, told Newsweek.
The features are layers of limestone sedimentary rock in Sweden, China and Russia that contain 100 to 1,000 times more meteorite debris than normally seen and are 465.7 million years old.
Another is a spike in the meteorite impact cratering rate—21 craters—from about 466 to 440 million years ago, with all of them forming fairly close to the equator. Normally they would be expected to be found anywhere on Earth, so, statistically, it is highly unusual.
There are also a large number of tsunami deposits recorded in sedimentary rocks at many locations from about 468 to 461 million years ago.
To come to this conclusion, the researchers calculated the area of the Earth at the time that would have been capable of preserving impact craters. They found that much of the Earth would have preserved craters if something had impacted, with only 30 percent of this suitable land located close to the equator. Despite this, all the impact craters are close to the equator.
"Normally asteroids coming from the asteroid belt impact the Earth randomly, so craters would be found anywhere on the Earth, at any latitude. We measured the amount of land mass at latitudes higher than 30 degrees (ie. towards the poles), and the amount closer to the equator, and found that 70 percent is at higher latitudes," Tomkins said.
"The odds of all of the impacts occurring in that 30 percent of near-equator land mass is very small (similar to tossing a three-sided coin for every crater and getting tails every time) if they had been on random orbits from the asteroid belt."
This distribution would be expected of debris hitting Earth from a ring, Tomkins said, and suggested in the paper that the odds were about one in 25 million it did not come from a such a formation.
The ancient asteroid must have come closer to the Earth than a distance known as the Roche limit, which is the minimum distance at which a celestial object, such as a moon or asteroid, can orbit a larger body (like a planet) without being torn apart by the larger body's tidal forces. The Roche limit varies depending on the size of the object and the mass of the planet.
A moon or large asteroid venturing too close to a planet and crossing its Roche limit is one of the most common ways rings form, with this being the way that Saturn's rings are thought to have originated.
This ancient ring around Earth may have blocked out some of the heat of the sun, possibly contributing to a major global cooling event known as the "Hirnantian Icehouse."
"What makes this finding even more intriguing is the potential climate implications of such a ring system," Tomkins said in a statement.
This cooling event occurred during the late Ordovician period, around 445–443 million years ago, and is characterized by a significant global glaciation that led to widespread ice sheets, especially over the southern supercontinent Gondwana, which was positioned near the South Pole during the Ordovician.
As one of the coldest periods in Earth's history, the Hirnantian Icehouse played a crucial role in the second-largest mass extinction in Earth's history, known as the Late Ordovician Mass Extinction, which wiped out roughly 85 percent of marine species.
"The idea that a ring system could have influenced global temperatures adds a new layer of complexity to our understanding of how extra-terrestrial events may have shaped Earth's climate," Tomkins said.
Do you have a tip on a science story that Newsweek should be covering? Do you have a question about ancient Earth? Let us know via science@newsweek.com.
References
Tomkins, A. G., Martin, E. L., & Cawood, P. A. (2024). Evidence suggesting that earth had a ring in the Ordovician. Earth and Planetary Science Letters, 646. https://doi.org/10.1016/j.epsl.2024.118991
View 0 Comments
Submit Correction
View Editorial & AI Guidelines