Gaseous hydrogen occurs in Nature in relatively small amounts. The earth's atmosphere contains about one part of hydrogen per 15000 to 20000 of air (in molecules number), although this proportion increases with altitude. The gases emited by volcanoes, charcoal mines and oil wells contain hydrogen.
Hydrogen is the most abundant element in the Universe. It is the main stellar and inter-stellar constituent. In the beginning of the 20th century, spectroscopical observations revealed the presence of hydogen in several nebula as well as in the sun's photosphere and chromosphere.
Hydrogen frequently appears combined with other elements. With oxygen it forms water, the most abundant substance in the earth's surface and principal constituent of animal and vegetal tissues. The elements oxygen, hydrogen and carbon are the base of all organic molecules.