Isotopic and Chemical Composition of Some Terrestrial Natural Gases

Abstract

A variety of natural gases was analyzed for their content of argon, helium, hydrogen, carbon dioxide, methane and heavier hydrocarbons, along with the isotopic compositions of their argon and carbon. It is found that most natural gases, including samples from geothermal areas, have a (He^4/A^( 40))rad ratio which is close to the production ratio in normal rocks. Glacial drift gases were found to have a distinctive chemistry and contain no detectable radiogenic argon. The observed atmospheric argon contents of all gases, including very high pressure sources, are found to be compatible with a simple solubility model. Using the measured ratios of (He^4/A ^(40))rad, a calculation of the mean life of He^4 in the atmosphere was made of 5 x 10^5 ≤ τ He^4 ≤ 2.5 x 10^7 years.