No. 16: Summer 1981
Although the Sm/Nd isotope ratios of the earth and the chondrites (a type of meteorite) seem pretty close in value, the possibility of a slight but significant discrepancy remains. If this small difference is confirmed, it would strongly imply that the earth's Sm/Nd ratio was shifted after the planet's formation. The most reasonable event that could shift this ratio is an long-debated earth-moon fission, wherein the earth's lighter surface material was somehow torn off to form the moon.
(DePaolo, Donald J.; "Nd Isotopic Studies: Some New Perspectives on Earth Structure and Evolution," Eos, 62:139, 1981.)
Comment. The moon's density is markedly less than the earth's, so the idea is not as wild as it seems.
|The hypothetical fission of Earth-Moon could have shifted the Nd isotope ratio in relation to that of the chondrites.|