There are various physical, chemical and biological processes that free up hydrogen from molecules (often hydrocarbons or water).
Once in the atmosphere, the hydrogen is lost to space (the Earth's gravity is too weak to hold onto it). So the Earth is losing hydrogen to space (perhaps at a very slow rate).
Is there any interaction between the Earth's atmosphere and high velocity protons in the solar wind (e.g. protons combining with atmospheric oxygen to form hydroxide) which is capable of balancing the hydrogen loss? How big is the hydrogen loss? Is the amount of hydrogen on Earth in equilibrium?