In the recent years, fluid inclusion research has been extensively applied to understand the role of fluids in the deep crust and crust-mantle interface. Fluid inclusions trapped within granulite facies rocks have provided important clues on the petrogenesis of dry granulite facies rocks through the influx of CO-rich fluids from sub-lithospheric sources. CO-rich fluid inclusions were also recorded from a number of ultra high temperature granulite facies terranes, suggesting the involvement of CO in extreme crustal metamorphism. Some recent studies speculate that CO derived by sub-solidus decarbonation reactions during extreme metamorphism has contributed to the deglaciation of the snowball Earth.