The Relative Abundance of the Isotopes of Potassium in Pacific Kelps and in Rocks of Different Geologic Age

The Dempster double focusing mass spectrograph has been used to determine the ${\mathrm{K}}^{39}$/${\mathrm{K}}^{41}$ isotope ratio in certain Pacific kelps, fossils, and rocks of different geologic age. Within the 1 percent accuracy obtainable, the potassium isotope ratio for the kelps and two Upper Cambrian fossils examined is the same as that of rocks. Rocks whose ages vary from Early pre-Cambrian to Tertiary show no measurable difference in the potassium isotope ratio, within 1 percent error. The average value of the potassium isotope ratio was found to be 14.12±0.28. Fluctuations in the ratio are attributed to isotope effects of the hot-filament ion source.