Image: Artist’s impression of Earth 466 million years ago and a possible ring. Credit: Oliver Hall
Australian scientists have discovered evidence that Earth once had a ring system. They are thought to have formed about 466 million years ago, at the start of a period marked by an unusual number of meteorite impacts. They suspect the reconstruction of plate tectonics at the time, particularly the locations of 21 impact craters. All of these craters lie within 30 degrees of the equator, even though more than 70 percent of Earth’s continental crust lies outside this region, an anomaly that current theories cannot explain.
The Australian researchers suspect that this well-defined impact pattern was created when a large asteroid flew past Earth and was shattered by the powerful tidal forces that occurred. This would have created a ring of debris around our planet, similar to Saturn’s rings. Over millions of years, material from this ring gradually fell to Earth, causing the number of meteorite impacts to increase. According to research leader Andy Tomkins, sedimentary rocks from this period contain an unusual amount of meteorite debris.
Global cooling
The formation of the debris ring may also have had consequences for our planet’s climate. According to researchers, its shadow may have led to a period of global cooling known as the Hirnantian Ice Age, the coldest period in Earth’s history over the past 500 million years.
Typically, meteorites land in random places on Earth, and impact craters are distributed roughly evenly across the planet. To investigate whether the distribution of impact craters during this period was higher than average near the equator, scientists calculated the extent of continental surfaces where craters from that period might have been preserved. Particular attention was paid to unaffected cratons with relatively old rocks that had not been buried by ice, sediment, or other disturbance. In the end, only about thirty percent of Earth’s surface was found suitable for preserving such craters, while all impact craters from this period were found in this region.
