Earth May Have Once Had a Saturn-Like Ring
Imagine a time when the Earth, 466 million years ago, was adorned with a ring system much like Saturn’s. This, according to a new study published in Earth and Planetary Science Letters, is a possible reality. This rings hypothesis not only sheds light on the celestial landscape surrounding Earth, but also explains a significant global cooling event known as the Hirnantian Icehouse, which saw average temperatures drop by 8°C (14.4°F).
The research, led by Dr. , a professor at Monash University in Australia, delves into the ancient Earth during the Ordovician period, a time when continents were predominantly clustered in the southern and lower northern hemispheres. During this era, life was flourishing in the oceans and seas with vertebrates, invertebrates, algae, and sea plants thriving, while the land remained devoid of life. Within this period, a 40 million year span known as the Ordovician Impact Spike saw the Earth bombarded with meteorites.
Evidence of these collisions lies in the high levels of —meteoric ingredients composed of silicates, sulphides, iron-nickel, and more—found in limestone from that period. While many of the impact craters have vanished due to ice cover, erosion, and tectonic activity, 21 of them remain, offering valuable insights.
Ancient craters are often preserved in geologically stable areas called —large regions with minimal geological change over time. Cratons exist globally, including in western Australia, North America, Greenland, Scandinavia, Siberia, India, Sri Lanka, southern Africa, and eastern South America. However, the position of these continents during the Ordovician period differed from their current locations. Tomkins and his colleagues noticed that all 21 preserved Ordovician craters were concentrated within 30 degrees of the equator at the time of the impacts, despite 70% of the ancient continents being outside this band.
Given the random nature of meteor showers, the probability of all surviving craters being clustered in this narrow latitude is statistically improbable. This observation suggests a force concentrating the incoming meteorites, and Tomkins and his colleagues believe they have identified that force: a ring system.
The conventional explanation for the Ordovician Impact Spike—a large body fragmenting in the asteroid belt and sending debris towards Earth—does not align with the crater location. The researchers propose a more fitting scenario: an intact asteroid escaping the asteroid belt and wandering towards the inner solar system. During its journey, it came close enough to Earth to be pulled apart by our planet’s , the boundary where Earth’s gravitational force dominates. This event created a flying rubble field that eventually settled into an orbiting ring around the Earth’s equator. This ring was temporary, eventually succumbing to Earth’s gravity and , pulling the debris down to the surface.
“Over millions of years, material from this ring gradually fell to Earth, creating the spike in meteorite impacts observed in the geological record,” said Tomkins in that accompanied the paper’s release. “We … see that layers in sedimentary rocks from this period contain extraordinary amounts of meteorite debris.”
Before the ring dissipated, it had a significant impact on Earth’s climate. The 23-degree tilt of Earth’s axis caused the ring to cast a shadow on the planet, leading to a global cooling effect. The collisions that brought the ring’s debris down to Earth kicked up dust, further increasing the darkness and contributing to the cooling.
“The idea that a ring system could have influenced global temperatures adds a new layer of complexity to our understanding of how extraterrestrial events may have shaped Earth’s climate,” said Tomkins.