elements, abundance of

elements, abundance of The relative amount of each element or isotope in a given object such as a planet, star, or galaxy. Cosmic abundance refers to the proportions in the Universe as a whole. The amount of an element may be expressed either as the number of atoms, or by mass. The standard cosmic abundance is based on that of the Solar System, which has been determined from the Sun's spectrum and from analysis of meteoric debris. The cosmic abundance is dominated by hydrogen, with about 25% helium by mass and all remaining elements amounting to less than 2%.

cosmic abundance of the most common elements
Element	Percentage abundance by mass	Percentage abundance by number of atoms
Hydrogen	73.5	92.1
Helium	24.9	7.8
Oxygen	0.73	0.061
Carbon	0.29	0.030
Iron	0.16	0.004
Neon	0.12	0.008
Nitrogen	0.10	0.008
Silicon	0.07	0.003
Magnesium	0.05	0.002
Sulphur	0.04	0.001
Argon	0.02	0.001
Nickel	0.01	0.0002