This Is the Oldest Known Chunk of Earth

Researchers have confirmed that a tiny sliver of zircon named 01JH36-69 is the oldest chunk of our planet ever identified. With 4.4 billion candles on its cake, the gem is barely younger than the planet itself. It measures only 200 microns by 400 microns, but what it lacks in size, it makes up for in scientific clout.

“Zircons older than 4.3Gyr old are extremely rare,” the team reported in their paper, published in Nature Geoscience yesterday. “So far, there are published secondary-ion mass spectrometry (SIMS) data from only four terrestrial zircons, all from the Yilgarn Craton of Western Australia.” 01JG36-69 is among this small data set, having been discovered in the Jack Hills region of the craton in 2001. Its age was initially estimated with the traditional method of radioactive uranium decay, which tentatively placed the gem on the short list of the world's oldest materials.

But some geologists suspected that these radiometric readings might provide a false date, due to contamination within the zircon crystal. One of their concerns was that alpha particles, which are released by the slow decay of uranium into lead, might create fissures within the crystals allowing it to be polluted with outside materials.

But the greater problem wasn't with outside materials getting into the crystal, but rather, its interior materials leaking out. Lead atoms are not locked in place within the zircon, and can sometimes make a break for freedom. The frustrating mobility of the atoms has thrown the accuracy of the specimen's radiometric results into question.

“If there's a process by where lead can move from one part of the crystal to another place, then the place where lead is concentrated will have an older apparent age and the place from where it moves will have a younger apparent age," explained John Valley, the study's lead author, to LiveScience.

To solve this problem, Valley and his team used the laborious technique of atom-probe tomography to double-check the sample's age. Essentially, this means they counted every lead atom and mapped its position within the zircon in order to determine if the sample had suffered enough interior damage to warp the radiometric readings. Thankfully, the original age was corroborated, rather than refuted.

“We've demonstrated this zircon is a closed geochemical system, and we've never been able to do that before,” Valley said. “There's no question that many zircons do suffer radiation damage, but I think relative to these [Jack Hills] zircons, this should settle it once and for all.”

Now that this Methuselah of a zircon has been confirmed to be the oldest surviving piece of the planet, scientists can, according to Valley's paper, provide “a basis for theories of crustal growth, tectonics, surface conditions and possible habitats for life on early Earth.”

For example, the zircon seems to support the theory of a cool primordial Earth, which may, in turn, push estimates of abiogenesis back many millions of years. “There is no reason why life could not have existed on Earth 4.3 billion years ago,” Valley told the Telegraph. “The zircons show us the earliest Earth was more like the Earth we know today. It wasn't an inhospitable place.”

Like any seasoned veteran of our planet, it turns out that 01JH36-69 has some great tales to tell.