Zircon crystals are the oldest rock pieces found on Earth. Contrary to past beliefs, these crystals may have been formed in the impact craters left by ancient asteroids, a new study has found.

Zircon crystals are about the width of a human hair. They are more than 4 billion years old. Putting it in perspective, our planet is just a little older than 4.5 billion years.

A decade ago, researchers said these ancient crystals could have developed during the collision of tectonic plates. However, current findings showed that the plate tectonics, as we understand the concept today, did not occur during the planet's early years.

To test the alternative asteroid crater theory, a team of researchers from Trinity College Dublin analyzed a relatively younger asteroid crater, the Sudbury impact crater in Ontario, Canada.

At approximately 2 billion years old, the Sudbury is the planet's second oldest and the best-preserved impact crater. In 2014, the team was able to collect thousands of zircon crystals from the crater, proving the asteroid impact crater theory.

The newly procured zircon crystals were analyzed at the Swedish Museum of Natural History. The analysis found that the new set had the same compositions with the ancient set. In fact, they were indistinguishable in terms of crystal compositions.

"Many people thought the very ancient zircon crystals couldn't have formed in impact craters, but we now know they could have," said first author Gavin Kenny, a researcher at the School of Natural Sciences in Trinity, highlighting the surprising find.

Zircon is so durable that it is capable of surviving various geological events. This characteristic turns zircon into "tiny time capsules" that can record many events in history in the span of hundreds of millions of years, yet its core remains unchanged.

"[Zircon is] the most reliable natural chronometer that we have when we want to look at the earliest part of Earth history," said Paul Mueller, a geology professor at the University of Florida.

Zircon contains uranium, a radioactive element that Mueller describes as "the clock within the zircon." After a specific period of time, uranium transforms into lead. This enables scientists to determine the age of zircon crystals.