[wycx]

The article refers to ancient surface, as in, the oldest place that we can find that has continuously been an exposed surface. The take away is that most areas don't remain stable at the surface, either they erode away, or get buried via sedimentation.

The article is in no way stating the oldest bit of the Earth's crust is 1.8 million years old. Crust has a specific meaning, the chemically differentiated rocks at the surface i.e. everything but the very very rare bits of exposed mantle. Oldest oceanic crust is <200 Ma, oldest continental crust dates to the Hadean (4.4 Ga, if you set the bar at only zircons).

[ianai]

All comments in a thread based on an article should be read in that context. Unless, of course, the links are never followed and we’re just here to massage each other’s preconceptions.