Step aside, space-aliens!
In past articles I have covered the 4-billion-year-old Gibeon meteorite, as well as ancient carbonado diamonds from space. These extraterrestrial visitors have over a billion years of age and seniority over Earth’s natural diamonds, which are a “mere” 1-3 billion-years-old.
That means when Mr. Gibeon and Mrs. Carbonado step onto the tram, polite diamonds give up their seats.
BUT… Do you know about the Jack Hills zircon?
The Jack Hills zircon, which I’ll address as “Mister Hills” out of respect, is Earth’s oldest native resident. A part of our planet’s crust which crystallized an astounding 4.4-billion-years ago, Mr. Hills is the oldest known native object.
Just think about that! As a species, humans have only existed for 200,000 years. That’s the blink of an eye for Mister Hills. Putting it into proper context, if we treat Mister Hills as being only 100-years old, all of human history has taken place during his last 40 hours!
Tiny but titanic
Researchers came across Mr. Hills in 2001 in a remote area of Western Australia he’s called home since time immemorial. Seen embedded in epoxy above, Mister Hills is only 400 micrometers tall. That’s about as high as four human hairs piled atop one another, just a bit bigger than a dust mite.
Coolest of the cool
Mister Hills has been kind enough to teach us a few things. Specifically, he redefined what we know about Earth’s history, strengthening the theory of a “cool early Earth.”
Trace elements in his zircon crystal appear to be from water-rich granite-like rocks such as granodiorite or tonalite. This suggests that the temperatures on Earth would have supported liquid water, making life possible far earlier than previously imagined. As Mason Inmam stated in Science Magazine:
The long-prevailing view, based largely on models of planet formation, was that Earth stayed hellishly hot for 500 million years, the Hadean Eon. But the oldest minerals found–hardy zircons from Australia’s Jack Hills, some of which formed when Earth was only 200 million years old–have suggested a much different picture.
Countless cousins
More than 100,000 similar zircons have been found in the Jack Hills area. There are many which are older than 3-billion-years-old but only three of them approach the 4.4-billion-year mark commanded by our friend Mister Hills.
The task of accurately dating such ancient objects is complex. Extreme age can render some conclusions suspect due to potential radiation damage during an object’s lifetime. Those interested in a technical dissertation involving cathodoluminescence imaging and 3D atom-probe mapping may be interested in this 2014 Live Science article by Becky Oskin, but the ultimate conclusion by researchers is that our friend Mister Hills appears to have his bona fides in order.
According to John Valley, a geochemist at the University of Wisconsin, Madison and lead author of the subject’s paper published by Nature Geoscience in February 2014:
We’ve proved that the chemical record inside these zircons is trustworthy… The zircons show us the earliest Earth was more like the Earth we know today. It wasn’t an inhospitable place.
Polite society
So be advised, Gibeon meteorite. We love you tons – and we love your tonnes of alien iron ore which have landed here on Earth. And you, dear Mrs. Carbonado, with your beautiful, dark and mysterious ways. Both of you are older than our planet’s diamonds, it’s true. And we’re grateful you chose to make our planet your home. But we do have one senior resident here, a simple Earth-born zircon, that deserves your respect.
We trust, should he step on your tram, that you’ll yield your seats.
