Geochemist Katharina Pahnke-May has a clear favourite among the elements: Neodymium.

"Neodymium is my absolute favourite! It has seven isotopes, with the isotope with mass 143 acting like a fingerprint for different regions on Earth. It therefore enables chemical oceanographers and palaeo-climatologists to reconstruct the input of rock material and dissolved ions. With the help of neodymium, we can trace transport routes in the sea, e.g. in surface and deep currents, for the present day and the geological past."