Mapping impact craters and considering how plate tectonics has changed the face of the Earth, researchers have found evidence suggesting that Earth may have had a ring system around 466 million years ago.
Of the over 200 impact craters known, 21 date to the Ordovician—the time period from 485.4 to 443.4 million years ago. If we consider the distribution of land and sea at the time (two large landmasses, named Laurentia and Gondwana, surrounded by an archipelago of smaller islands), all these craters are located within 30 degrees of the equator.
In a new study, the authors argue that his localized impact pattern was produced after a large asteroid had a close encounter with Earth. Stretched by the planet’s gravity, the asteroid broke apart, forming a debris ring around the Earth.
The authors used crater age estimates and other evidence, like traces of extraterrestrial material preserved in sediments or rocks shattered by a collision, to create an impact time-line for the entire Ordovician. This shows that the impacts cluster in a relatively short interval of 50 million years.
“Over millions of years, material from this ring gradually fell to Earth, creating the spike in meteorite impacts observed in the geological record,” says lead study author Professor Andy Tomkins, from Monash University’s School of Earth, Atmosphere and Environment.
This intriguing hypothesis could also explain another mystery. The Hirnantian is a major glaciation lasting from approximately 460 to around 420 million years. It was the coldest period in the last 500 million years of Earth’s history. Geologists don’t know the exact causes behind the Hirnantian glaciation; possible explanations include a drop in greenhouse gases and Earth’s atmosphere trapping less heat, volcanic dust blocking the sunlight, or an impact winter. The authors of the new study speculate that the ring could have cast a shadow on Earth, cooling Earth’s surface and triggering an ice-age.
“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,” concludes Professor Tomkins in an interview published by the Conversation.
The full study “Evidence suggesting that Earth had a ring in the Ordovician” was published in the journal Earth and Planetary Science Letters and and can be found online here.
Additional material and interviews provided by Monash University.
