Finding the oldest rocks on Earth is important because they should help scientists solve one of geology’s great mysteries: how the surface of our planet was transformed from the ocean of magma that existed in the Hadean – the earliest era in Earth’s history – into the floating tectonic plates we have today.
For the last four years, Jonathan O’Neil of Mc Gill University and colleagues have been studying a large band of ancient rocks in northern Quebec known as the Nuvvuagittuq greenstone belt.
Most people think that radioactive dating has proven the earth is billions of years old.
However, because Sm and Nd have very similar chemical properties (unlike Rb and Sr), large ranges of Sm/Nd in whole-rock systems are rare, and in particular, low Sm/Nd ratios near the y axis are very rare.
Therefore, because of the difficulty of obtaining a wide range of Sm/Nd ratios from a single rock body, and because of the greater technical demands of Nd isotope analysis, the Sm Sr isochrons had proved unsatisfactory.
The main challenge of Sm-Nd dating is accurately determining the ratios between the different isotopes of neodymium, specifically Nd-144: Nd-143 and Nd-144: Nd-142.
Nd-144 is a naturally-occurring isotope of neodymium and so its relative abundance compared with the two isotopes produced by the radioactive decay of samarium can reveal the extent of that decay.
Yet this view is based on a misunderstanding of how radiometric dating works.