original_query: What is the focus of research interests in using naturally occurring isotope variations?
query: What is Donald J. DePaolo's focus of research interests in using naturally occurring isotope variations?
answer: DePaolo's research focuses on using naturally occurring isotope variations to explore questions such as the origin of deep-source Hawaiian plume and other hotspots, tracking fluids moving through groundwater systems, understanding isotope fractionation of molten materials, magma chamber processes, and isotopic evidence for detecting life on other planets.