Earth may have had a ring system similar to that of Saturn about 466 million years ago. To propose this hypothesis a recent study published in the journal Earth and Planetary Science Letters from Andrew Tomkins, Erin Martin And Peter Cawood of Monash University in Australia. According to the study, the rings would have been generated by the gravitational capture of a asteroid on the part of our planet: the celestial body would have shattered from the tidal forces exerted by the Earth and the orbiting debris would have organized itself into a band of rings. The presence of the ring system could have influenced the Earth’s climate contributing to theHirnantian Ice Agewhich in turn helped trigger the first mass extinction.
The hypothesis is based on the analysis of 21 impact craters products from theOrdovician meteoric eventa period between 485 and 443 million years ago in which the Earth has been subjected to a intense meteor bombardmentThe distribution of the craters, their dating and chemical-physical characteristics are compatible with the presence of a ring of debris around our planet, made up of meteorite fragments which, falling back to Earth over millions of years, created the meteorite impact spike observed in the geological record. Although the hypothesis is compatible with the geological dating, the data they are not yet sufficient to say with certainty that the Earth had rings, so further studies are needed to confirm or deny this fascinating possibility.
Evidence of Ancient Uranus-Like Rings Around Earth
The hypothesis of Tomkins, Martin and Cawood is based on the examination of paleogeographic records of the impact craters produced by theOrdovician meteoric eventa period in the Earth’s geological history characterized by an iintense meteor bombardment. In particular, the researchers focused on theanalysis of the distribution on the earth’s surface Of 21 impact craters produced during the Ordovician meteoric event.
If these 21 craters were generated by the impact of asteroids from the main asteroid belt between Mars and Jupiter, then they should be distributed completely randomly on the Earth’s surface. In normal circumstances, in fact, asteroids can strike randomly at any latitude, as seen for example on the Moon, Mars and Mercury. In the case in which the 21 craters were generated from a single body which shattered during a close encounter with Earth, then their distribution Not will be random, but “concentrated” in specific areas of the Earth’s surface.
What Geological Surveys Say About the Earth’s Crust
In order to determine with certainty the distribution of the 21 craters, the researchers had to use different plate tectonic models available for the period Ordovician (485 and 443 million years ago). The Earth’s crust has not remained still during these 400 million years, so it is necessary reconstruct the position that they had in the past, identifying the paleo-latitudes of the areas that preserve such craters, called cratons. These represent areas that have not undergone major geological changes for hundreds of millions of years.
Taking this into account, the researchers found that the 21 craters were all located in a band of about 30 degrees from the equatorconsequently they were not distributed randomly, but in a correlated manner among themselves. This arrangement can be explained by assuming that the Earth had in the past a ring of debris around it, since such rings typically form above the equator of the planets.
How the rings around Earth would have formed
The most likely hypothesis for the formation of this ring of debris around the Earth’s equator is that of capture of a large asteroid by the Earth’s gravitational field. Once captured, the asteroid was attracted towards the planet, passing the so-called Roche limitthat is, the minimum distance below which the Earth’s tidal forces disintegrate a body in orbit. This passage caused the asteroid disintegrationgenerating a ring of debris around the Earth similar to that possessed today by Saturn and other gas giants such as Jupiter, Uranus and Neptune (although the latter are less conspicuous). It is supposed that the progenitor asteroid of the rings could have had a diameter of about 12.5 km. Since such an event should have happened 466 million years ago and that the age of Saturn’s rings is about 400 million years, the title of “lord of the rings” may have belonged to Earth in the past, rather than Saturn.
The possible consequences of the rings: ice age and mass extinction
Debris rings are not stablebut tend to disappear over time. Over the millions of years following its formation, the material of the ringsmade up of dust, ice and rock fragments, it is deorbitedimpacting the Earth’s surface in the equatorial zone, giving rise to the Ordovician impact peak. Further supporting this scenario, geological analyses of sedimentary rock layers from this period show extraordinary amounts of meteorite debris, the so-called L-type chondrites.
The rings may have had an additional effect. Being at the equator, and the Earth’s axis being tilted, the rings may have created a band of shadow on the Earth’s surface that blocked most of the incoming sunlight flow tens of millions of yearsSuch shading may have contributed to the so-called Hirnantian Ice Agea period characterized by a dramatic cooling of our planetThe coldest period of the last half billion yearswhich led to one of the five great mass extinction events in Earth’s history.
