True ages of rocks might be distorted through Earth's history

Giga year old zircon crystals still contain lead in form of nanometre size spheres of pure lead. However, the inhomogeneous spatial distribution of the lead spheres might falsify ages determined from high-resolution Pb isotope measurement with ion probe.

Zircon is an ideal mineral for age determination of very old rocks because it is believed to be a closed system during Earth history. Zircon geochronology thus is a standard method of geological age determination. Recently, an international group of earth scientists studied zircon from 3.4 billion years old high-temperature metamorphic rocks from Antarctica with transmission electron microscopy TEM at the GFZ German Research Centre for Geosciences.

TEM investigations revealed that the lead from radioactive decay was not homogeneously distributed in zircon but was accumulated withinin inhomogeneously distributed Pb nano-spheres in zircon with only 5 to 30 nm in diameter. The inhomogeneous distribution of lead in zircon might adulterate the ages measured with high-spatial resolution ion probe technique.