Researchers may have found the origin of Earth's oldest crystals, discovering tiny crystals that likely formed in huge impact craters not long after our planet formed about 4 billion years ago.
Rocks that formed over the course of Earth's history allow researchers to understand when water first appeared on the planet, how Earth's climate has varied over time, and even when life first began. With that said, it's only possible to go back so far in time with rocks. This is largely because the only material that is currently present from very early Earth comes in the form of tiny, naturally occurring zircon crystals.
The origin of these crystals, though, has been a cause for major debate. They're about the width of a human hair and formed more than four billion years ago. Researchers have argued that they may have formed when tectonic plates on Earth's surfaces collided with each other. However, new evidence may suggest another explanation.
In this latest study, the researchers suggest that the tiny crystals may have formed in huge impact craters that were produced as asteroids and meteorites slammed into a young Earth. To test this theory, they decided to study a much younger impact crater to see if zircon crystals similar to the very old ones could have possibly formed among these violent conditions.
So, what did they find? The researchers collected thousands of zircons from the Sudbury impact crater in Ontario, Canada. This is the best preserved large impact crater on Earth and the planet's second oldest confirmed crater at a staggering 2 billion years old.
The researchers then analyzed the crystals and found that the crystal compositions were indistinguishable from the ancient set of crystals. This, in particular, shows that zircons may have formed from impacts on early Earth, which shows that our planet may have had more of a violent history than we first thought.
"What we found was quite surprising," said Gavin Kenny of Trinity's School of Natural Sciences and first author of the study. "Many people thought the ancient zircon crystals couldn't have formed in impact craters, but we now know they could have."
The results reveal a bit more about these crystals and also tell researchers a bit more about our early Earth.
The findings were published in the April 2016 issue of the journal Geology.
