GS Paper - II

The rings of Saturn are perhaps the most stunning features of the Solar System. Earth may once have boasted something similar, a study published in the journal Earth and Planetary Science Letters found. The existence of such a ring, forming around 466 million years ago and persisting for a few tens of millions of years, could explain several puzzles in our planet’s past, Andrew Tomkins, a professor of planetary science at Monash University in Australia, and the study’s lead author, wrote in The Conversation.

Asteroid debris

• Earth’s ring would have been like the rings seen today around Jupiter, Saturn, Neptune, and Uranus. It formed when an asteroid passed too close to Earth, was stretched by its gravity to the point it broke down into lots of small and large pieces.
• These pieces jostled around and gradually evolved into a debris-laden ring orbiting Earth’s equator.
• However, over time the material from the ring was pulled towards Earth, once again courtesy gravity. While most of the smaller pieces would have been burnt up in the planet’s atmosphere, the larger pieces would have formed impact craters on Earth surface, close to the equator.
• It is these impact craters that led the Monash scientists to discover the existence of a ring around Earth.
• Analysis of 21 crater sites dated to between 488 million and 443 million years ago to the Ordovician period, found that the impacts all occurred close to the equator.
• Under normal circumstances, asteroids hitting Earth can hit at any latitude, at random, as we see in craters on the moon, Mars and Mercury.

A giant parasol

• A ring over Earth’s equator would have had a profound impact on the planet in more ways than one. Crucially, the axial tilt of Earth relative to the Sun would mean that such a ring would shade winter hemispheres of the planet, while slightly increasing solar flux — amount of solar energy to reach Earth — to the summer hemispheres.
• This could accentuate winter cooling while slightly increasing summer heating. Overall, scientists theorise that a ring would lead to global cooling by effectively acting as a giant parasol.
• Interestingly, the period in which the ring existed Earth did witness dramatic cooling. Around 460-465 million years ago, mean temperatures in Earth plummeted dramatically.
• By 445 million years ago Earth was seeing the peak of the Hirnantian Ice Age, the coldest period in the past half a billion years.
• Was the ring responsible for this cooling? Possibly. But more research is needed to say for sure.

• The next step in our scientific sleuthing is to make mathematical models of how asteroids break up and disperse, and how the resulting ring evolves over time.