Oldest fragments of the Earth

Tiny, diamond-like crystals of zircon (ZrSiO4) from the Jack Hills in Western Australia are the oldest minerals so far dated on Earth. A landmark study, published in 2001, used a technique called Uranium-Lead (U-Pb) dating to date the formation of one of these zircon crystals to 4.404 billion years ago (±0.008 billion years/8 million years). Later studies questioned these findings, with alternative readings of the data that knocked as much as 100 million years off the age estimate. The debate was seemingly settled in 2014, when another study used atom-probe tomography to test the validity of some alternative readings of the data. This study provided a new, more precise age estimate of 4.374 billion years (±0.006 bya/6 million years). This means that these zircons formed only around 160 million years after Earth itself was formed.

Uranium-lead dating is a technique primarily used to date zircon crystals. It works by comparing the ratio of uranium to lead atoms in the crystal structure. Lead is not a component of zircon, so any lead present in the crystal can only have come from the radioactive decay of the uranium atoms, which takes place at a broadly constant rate.

These ancient zircon crystals are thought to have been formed in impact craters on the surface of the early Earth. The ones in the Jack Hills are embedded in much younger sedimentary rocks, having been eroded from primordial rocks billions of years ago.