Hydrogen gas is much lighter than air, and it rises fast and is quickly ejected from the atmosphere. This is why hydrogen as a gas (H2) is not found by itself on earth. It is found only in compound form with other elements. Hydrogen combined with oxygen, is water (H2O). Hydrogen combined with carbon forms different compounds like methane (CH4), coal, and petroleum. Hydrogen is found in all growing things. It is also an abundant element in the earth's crust.