Hydrogen is a very important element for humans because it is one of the elements that comprises water, or H2O. It exists in human bodies and is used for a variety of important technologies as a renewable energy source and for other applications. Hydrogen is also considered by scientists to be one of the most commonly found elements in our universe as it comprises an estimated 75 percent of the entire universe's elemental mass.
It is thought that most stars in the universe are actually comprised mostly of hydrogen, and the sun, which feeds the Earth its solar energy and heat, is no exception. Hydrogen is a highly flammable substance and a great source of energy. The various space shuttle engine ran on hydrogen. Hydrogen has also been used in lamps, balloons, as a coolant for batteries and even some of the world's most deadly weapons, namely the hydrogen bomb.
Hydrogen is a useful energy source because it burns very cleanly, unlike fossil fuels and other energy sources. It does emit some dangerous gases, but it doesn't have any carbon emissions, which is a very important advantage.
Hydrogen fuel cells, in particular, is a technology that scientists believe could lead to transportation no longer producing emissions. There are already cars that exist that use this technology. As these cars operate, the only thing they emit is water.