They say diamonds are forever, but nothing lasts as long as zircon. It’s literally older than life on Earth, older than trees, older than plankton, and even older than the single-celled organisms that started it all. With recent developments and discoveries, scientists have learned a lot more about the early stages of our planet, thanks to zircon. But how might zircons help scientists study early earth? So, let’s get digging and take a look back in time to learn what a gemstone can teach us about when Earth was still in its infancy.
The mineral we’re interested in today is called zircon, scientifically known as zirconium silicate.
Where Are Zircon Crystals Found?
It can be found abundantly in the Earth’s crust, although crystals are usually under a millimeter in size.
Chemical Formula For Zircon
The chemical formula for zircon is RSiO4.
While it may be brittle, zircon is chemically stable and can survive weathering. Most importantly, for our purposes, it contains uranium. We’ll get to that in a minute.
How Old Is Zircon?
So, how old is zircon? These gems have been forming since the Earth was about 200 million years old, before Pangaea was even formed.
They have survived eons of pressure, heat, and tectonic shifts, giving us an idea of what Earth was like three to four billion years ago.
Moreover, geological events can leave a ring in the zircon as more material grows over it, similar to rings in a tree. Each ring has a story to tell, with the rings closer to the center reaching even further back in time.
Now, remember when I mentioned zircon’s uranium content? This radioactive element has helped scientists determine the age of zircon specimens. However, the process is arduous.
First, they have to extract the tiny zircon crystals from their host rock, which let’s say is granite. The granite is broken up into individual mineral grains, and since zircon is denser than the other minerals, the rubble is placed in a vat of super dense fluid. All the other minerals float, while zircon sinks to the bottom.
Scientists then take one of these zircon crystals and slice it into pieces that are only about a micrometer thick, roughly the width of a human hair. This allows for a clear view of growth rings and other clues about the changing geological conditions the crystal experienced during its formation.
Next, the scientists study the uranium within the zircon. By examining the uranium isotopes, which have a half-life of about four and a half billion years, they can date the crystals within a range that was impossible to achieve through carbon-14 dating, which can only reach back a little under 6,000 years due to its much shorter half-life.
After sorting through countless zircon crystals, scientists found specimens ranging in age from 3 billion to 4.4 billion years old.
While we have uranium to thank for our ability to date these minerals, it also made dating the older specimens more challenging. Here’s why: the decay of uranium releases alpha particles that can damage the crystals, allowing foreign elements to seep in over time and affect the accuracy of the readings.
Uranium can also move around within the zircon or even escape the crystal entirely, further casting doubt on the accuracy of these crystals as chronometers and the trustworthiness of their internal chemical record.
However, the team hopes to prove the reliability of the zircon by individually counting the lead atoms in their oldest specimen and showing that the lead hasn’t gone anywhere.
Imagine being forced to count the blades of grass in your yard! These ancient Australian zircon crystals were found to have trace elements that hint at a much different geological landscape of early Earth than we previously believed.
The findings suggest that the zircon formed in water-rich granite-like rocks, such as grandidorite or tonalite, implying that the Earth may have cooled down enough to allow surface water much more quickly than we thought.
That could mean our Earth was not the totally inhospitable wasteland we thought it was, but may have been more similar to how it is now.
The Oldest Rock
There’s a rock formation jutting unassumingly out of the Canadian Northwest Territories that is believed by many to be the oldest rock on Earth.
Due to billions of years of tectonic shift, most of the Earth’s original crust has been melted and recycled. However, this particular nice formation may be the closest thing to Earth’s original crust that exists today.
Normally, geologists would use zircon to date rocks, just like they did in Australia. But in this case, they couldn’t find any zircon, so they had to use different isotopes and some educated guesses until they found a few crumbs of zircon. It’s like finding a needle in a haystack or, rather, a zircon in a nice stack.
Hope you this post about how might zircons help scientists study early earth may help you. Tell me, would you count the blades of grass in your yard just to appease the HOA?