The Reading Rainbow guy in Star Trek Next Generation was born blind, but able to see through his VISOR and, later on, via prosthetic ocular implants. By analogy, field geochemists now have new vision.
Although, the device is not installed in a visor or as a prosthetic ocular implant, the new generation of energy-dispersive X-Ray Fluorescence spectrometers are battery-driven and portable in the field. “The gun” measures x-rays emitted from the sample and converts the signal intensity to elemental concentrations.
Perhaps counterintuitive, the most common elements on Earth cannot be measured (hydrogen, oxygen, carbon and nitrogen, but trace elements such as molybdenum (Mo) are reliably determined due to the distinct energy of the emitted x-ray photons from heavier elements.
Based on a compilation of more than 300 sediment cores deposited under a wide range of environmental conditions in the modern ocean, we broadly confirm a recent suggestion by Scott & Lyons that anoxic and sulfidic basins leave high molybdenum contents in the sediments. Moreover, we conclude that organic-rich sediments with high Mo enrichments are most likely deposited in basins with anoxic and sulfidic bottom waters. Thus, the Mo signature can be applied to the geological record to identify anoxic and sulfidic oceans in the past.
Access the data of sedimentary Mo contents here
Dahl et al. Chem. Geol. (2013): Tracing euxinia by molybdenum concentrations in sediments using handheld X-ray fluorescence spectroscopy (HHXRF)