Scientists investigated whether Earth used to have a ring around it and how this would have affected our planet millions of years ago.
Introduction
Have you ever seen a shooting star? Well, shooting stars are actually pieces of rock from space called meteors. Meteors that make it through the Earth’s atmosphere and fall to the ground are called meteorites. When they hit the Earth, they are traveling fast enough that they may leave a large hole. These holes caused by meteorite crashes are called impact craters.
Millions of years ago, there was a time where there were lots more meteorites falling to Earth than usual. We call this time the Ordovician period (pronounced or-doh-VISH-ee-un). Geologists found something interesting when they investigated limestone rocks from the Ordovician period. Limestone rocks are generally well-preserved throughout geological history. This means some limestone rocks have been around for hundreds of millions of years! Scientists have examined limestone rocks in several places around the world and found lots of stony meteorites of a type known as “L chondrite”. But why are there so many of these meteorites in these old rocks? We think a giant L chondrite asteroid was ripped apart by tidal forces as it passed too close to Earth! The resulting pieces formed a debris ring around the Earth.
We wanted to explore the impact craters from millions of years ago. This would help us to understand if there actually could have been a ring around the world!
Methods
We studied impact craters from the Ordovician period to look for evidence of whether Earth used to have a ring. We looked at these impact craters in a few different ways. First, we modeled the world’s geography and the distribution of tectonic plates during the Ordovician period. We did this with computer programs and by looking at data from the past. Tectonic plates move slowly over time, so millions of years ago, the Earth looked very different!
Next, we needed to be sure that we picked the best-preserved impact craters from the correct time. This would help us get the most accurate results. We chose places that have not changed much over millions of years. Some examples are places with less erosion and fewer mountains.
Finally, we wanted to analyze the distribution of these craters in more detail. We looked at the impact craters spread around the world to see if they followed a pattern. If they were just spread randomly around the world, then a ring around the Earth wouldn’t be likely. We used special calculations to work out this pattern. We also compared these ancient impact craters to more recent ones.
Results
We found that the impact craters from the Ordovician period did follow a pattern (Figure 1). They were not randomly distributed around the world. We found that these craters were often found in clusters. These craters were often found in areas that were around the middle of the Earth, nearer the Equator.
Discussion
The pattern of impact craters near the Equator does suggest that Earth might have had a ring. We think the answer is that an asteroid broke apart as it came very close to our planet! Earth’s gravity would have captured the debris after the asteroid broke up, and then this debris would have migrated to form a ring around the Earth’s equator. The rings around Jupiter, Saturn, Uranus and Neptune are all positioned around their respective equators.
Over time, Earth’s ring would have decayed. That means the pieces of the asteroid would have fallen to Earth as meteors and meteorites. This explains why there is so much L chondrite meteorite material in the limestone rocks. It also explains why the impact craters are near the Equator.
If such a ring existed, the fact that Earth is tilted relative to the Sun may have caused the global climate to change, too. A ring would have blocked the sunlight and created a shadow on the Earth. Getting less light would mean the cold places would have gotten even colder. This idea might explain a global cooling event that happened shortly after the impact craters formed during the Ordovician period.
Conclusion
Studying rocks can help us to understand how our planet looked millions of years ago! Have you ever examined an interesting rock and thought about where it came from? We should all keep asking these questions and be as creative as possible with our ideas. Our experiment shows that you can investigate anything. Even if it happened long before we existed!
