Understanding the earth processes that control lithium is key to exploration and developing the resources needed for society and the energy transition.   The lightest of the metals, lithium moves easily in fluids and is found in a variety of geologic environments from brines to pegmatites to clays.   Host Anne Thompson explores the geoscience of lithium, assessing what we know and what are the challenges in the quest to supply the lithium needed by human society. Our three guests provide insights into the variety of lithium sources that potentially allow for geographically distributed supply.  We talked first to Rebecca Paisley, a geochemist with WSP Canada, to consider the diversity of lithium bearing brines and the fundamental nature of the metal.  Its natural affinity to partition into the liquid phase means that lithium occurs in salty salar brines, a variety of geothermal brines and oil field brines.  The value of your brine, however, also depends on the end-product required and the steps needed to extract it from the solution.  Rebecca connects the value of lithium in brines to the whole mining circle.  Bob Linnen, Chief Geologist – Lithium, KoBold Metals, spent his academic career studying pegmatites and now continues to develop his ideas through global exploration.  The high grades in lithium pegmatites make them appealing targets for exploration, and better positioned to survive big fluctuations in commodity price.  Not all pegmatites, however, are created equal and much is still being learned about this important host for lithium resources as the mineral system view evolves. Koopmans et al., 2023 Lastly, we talked to Tom Benson, VP Global Exploration for Lithium Argentina.  Tom thought he was going to be an academic after completing a PhD on Thacker Pass, Nevada, USA, but an opportunity to engage in research and exploration was too good to pass up.  His work includes active collaboration with researchers around the world as well as exploration for new deposits.  Tom frames the occurrence of lithium in clays at Thacker Pass within the context of volcano-sedimentary systems.  The deposit has unique features, including the presence of higher grade illite in addition to lithium-bearing smectite.   Benson et al., 2023 New research globally focused on lithium resources continues to push our understanding and highlight the importance of its volatile nature in the ways in which it is concentrated and trapped.   Next week is the last episode of Season 4 – we will head to Namibia, host to the SEG 2024 conference September 27-30,  to explore the diverse geology and mineral deposits and hear about what the conference has in store.   Many thanks to our season 4 sponsor, Anglo American. Our theme music is Confluence, by Eastwinds.  SEG 2024 will be in Windhoek, Namibia!  Come join us in a country known for its spectacular and diverse geology  27- 30 September, 2024. The deadline is coming up soon for the SEG Student Chapter Podcast Challenge - 29 March 2024 - let's get it done!