The central problem is that the Earth doesn't preserve any rocks of that age, so geologists must rely exclusively on the oldest Hadean materials that are preserved: the Jack Hills zircon from the remote outback of Western Australia. Not surprisingly, the Jack Hills zircon has been both lauded and questioned for containing (or not) potential evidence of Earth's earliest signs of sediments and plate tectonics.

For years, geologists have tried to determine whether or not the Jack Hills zircon crystallized from a sediment-bearing magma. Granitic magma containing sediments is known as sediment-derived, or "S-type," granite. But so far, using traditional geochemical proxies, the results have been mixed.

A traditional discrimination diagram using a small handful of trace elements has been used to argue for only rare, or almost no S-type granites on early Earth. At low phosphorus (P) contents, however, the different types of zircon sources unfortunately overlap, which is particularly problematic because low-P zircons make up >95% of the oldest detrital zircons. Clearly, more zircon trace element information is needed.

In a study published in the journal PNAS, a research team led by Prof. Ross Mitchell from the Institute of Geology and Geophysics of the Chinese Academy of Sciences (IGGCAS) has addressed this problem by applying a precise machine learning method to recognize Hadean S-type zircon. This new approach distinguishes S-type zircon from non-S-type zircon, especially with the ability to identify low-P S-type zircon in the Hadean.