Helium

https://www.getscience.com/content/helium-medical-mission-critical http://www.forbes.com/sites/bridaineparnell/2016/06/28/scientists-find-helium-gas/#7a6e09ec326d http://www.forbes.com/sites/startswithabang/2016/06/29/how-does-helium-get-underground-in-the-first-place/#45414b623ec9 https://www.wired.com/2016/06/dire-helium-shortage-vastly-inflated/