They state in their Nature article: “The Moon is thought to have formed from debris ejected by a giant impact with the early 'proto'-Earth and, as a result of the high energies involved, the Moon would have melted to form a magma ocean. The timescales for formation and solidification of the Moon can be quantified by using ¹⁸²Hf–¹⁸²W and ¹⁴⁶Sm–¹⁴²Nd chronometry, but these methods have yielded contradicting results. In earlier studies, ¹⁸²W anomalies in lunar rocks were attributed to decay of ¹⁸²Hf within the lunar mantle and were used to infer that the Moon solidified within the first ~60 million years of the Solar System. However, the dominant ¹⁸²W component in most lunar rocks reflects cosmogenic production mainly by neutron capture of ¹⁸¹Ta during cosmic-ray exposure of the lunar surface, compromising a reliable interpretation in terms of ¹⁸²Hf–¹⁸²W chronometry.”