Researchers from Trinity College have established where our planet’s oldest rocks (zircon crystals) came from: loads and loads of asteroids.
Let’s start at the beginning. Earth’s oldest rocks are more than 4bn years old. Earth itself is 4.5bn years old.
The rocks are tiny, about the width of a human hair, and are ‘naturally occurring’. Their importance lies in their age. As they are from a time when Earth was very young, finding out about them allows us to learn about our planet’s nascent time.
The problem is, we don’t know where on Earth they came from. Well, we didn’t know, until Gavin Kenny from Trinity College Dublin got a team together and, with the help of the Irish Research Council and Science Foundation Ireland, got studying.
The original theory was that our tectonic plates rubbing together created these rocks, however, according to Kenny, that can’t be, as the crystals predate the collision of tectonic plates on Earth. So, what other possibility was there?
The answer had to be asteroids. Kenny and his team collected thousands of zircons from the 2bn-year-old Sudbury impact crater in Ontario, Canada – the best preserved large impact crater on Earth.
They then took a closer look at the zircon crystals and realised their composition was identical to older examples found elsewhere, meaning it’s possible they were deposited on impact. “What we found was quite surprising,” said Kenny, whose paper appears in Geology.
“There’s a lot we still don’t fully understand about these little guys, but it looks like we may now be able to form a more coherent story of Earth’s early years – one which fits with the idea that our planet suffered far more frequent bombardment from asteroids early on than it has in relatively recent times.”
Main asteroid image via Shutterstock