User: Given these paragraphs about Natural hydrogen, what are some of its sources?
Assistant: degassing of deep hydrogen from the Earth's crust and mantle; reaction of water with ultrabasic rocks (serpentinisation); contact of water with reducing agents in the Earth's mantle; interaction of water with freshly exposed rock surfaces (weathering); decomposition of hydroxyl ions in the structure of minerals; Natural radiolysis of water; decomposition of organic matter; biological activity; Extraction; Natural hydrogen is extracted from wells, mixed with other gases such as nitrogen or helium.