Tungsten Isotopes and the Beginning of Plate Tectonics 

Super correspondent also sent the link to THIS ARTICLE. It describes, in a remarkably simple way, the use of tungsten isotope tungsten-182 to determine the start of plate tectonics about 3.2 billion years ago. Give or take 100 million years.

Tungsten-182 is formed from the radio-active decay of hafnium-182 within 60 million years of the formation of the solar system. Find a lot of tungsten-182 compared to the other tungsten isotopes and the rock concerned had not been churned by subduction.

So find rocks to which nothing much has happened in the last few billion years. That, of course, means the Yilgarn of Western Australia where nothing much geological happens.

All this sounds rather straightforward, but actually doing it is not easy - neither in the bush or in the laboratory. The article tells the story well.

Collecting specimens in the Yilgarn.