Measuring just 200 by 400 microns (about 10 times the width of a human hair on its widest dimension), one would think finding an ancient zircon to be harder than finding a needle in the proverbial haystack…Or, in this case, like finding a nearly microscopic gemstone on a sheep farm in Western Australia. But geologists treasure such finds, even more than the rarest of gemstones. This is because such minerals contain clues to our planet’s beginnings.
According to the geologists that found it, the tiny zircon crystal is 4.4 billion year old. As the age of our planet is estimated to be around 4.5 billion years, that means that the tiny crystal was formed barely 100 million years after our planet (and its outer crust layer) was formed — and just 160 million years after the entire solar system was formed!
Such crystals are typically formed in the Earth’s crustal layers, and, under cooler geologic conditions. Thus, this early date would seem to indicate that our planet’s crust formed much earlier than previously theorized. Also, it lends strong support to the ‘cool early Earth’ theory in which much milder temperatures predominated and so could sustain large surface oceans — even possibly primordial lifeforms — relatively shortly after forming.
Geosciences professor John Valley (University of Wisconsin) and leader of the geologic survey that found the zircon, believes that the find indicates our early Earth was not quite as harsh and/or inhosptiable a place (for liquid water, and thus even primitive unicellular lifeforms) as other theories have suggested suggest.
“We have no evidence that life existed then. We have no evidence that it didn’t. But there is no reason why life could not have existed on Earth 4.3bn years ago,” said Valley in a press statement.
This early period in ourt planet’s geologic history is known as the Hadean Aeon (after the Greek god of the underworld, Hades). It is so named becasue it is widely accepted that the Earth formed from a relateively spheroid mass of molten rock (hot iron, mostly) — the very conditons one might expect in Hades. But according to this newer thoery, the Earth cooled down quite rapidly (within that 100 million year time span) and so coudl support liquid water at a much early time (other wise, was water may have formed would have quickly evaporated; the Earth being the equivalnet of a geological steam bath).
To determine and verify the age of the crystal, the geological team used two dating methods;the first was a standard dating technique based upon the radioactive decay of uranium to lead in a mineral/crystal matrix. However, because lead atoms can move through the crystal over time, they can give a false date. So, the team also conducted a more advanced test using a technique called atom-probe tomography. This technique permits measurement of the mass of individual atoms of lead within the crystal, and the two measurments together confirmed the age of the crystal at 4.4 billion years.
The oldest fossilized life forms known on our planet are stromatolites — structures formed by archaic, bacteria-like microbes — dating to 3.4 billion years.
The crystal find and analysis was published in a recent edition of Nature Geoscience,
Top Photo: A 4.4 billion year old zircon cdrystal is from the Jack Hills region of Australia and is now confirmed to be the oldest bit of Earth’s crust. Photograph: John W. Valley, University of Wisconsin via Science Insider
Some source material for this post came the Science Insider piece ‘Oldest Piece of Earth Discovered’ and additonal material (quote) from the Guardian article ‘Gem discovered on Australian sheep farm is oldest piece of the planet’