The oxygen-isotopic composition of Earth and Mars

The small difference between the O-isotopic mass fractionation lines of the Earth and Mars has been measured precisely using a laser fluorination syst em. The precision achieved from the two sample sets is better than +/- 0.01 4%, with the offset (Delta(17)O) between Mars and Earth measured as +0.321% . This result shows that all the Shergotty-Nakhla-Chassigny (SNC) meteorite s define a high level of isotopic homogeneity, comparable to that of crusta l material on the Earth, indicating that these meteorites originate, unequi vocally, from a single, common parent body (Mars). Allan Hills 84001, with its ancient age (4.56 Ga), shows that any initial heterogeneity imparted in to Mars from the nebula was homogenised very early in the formation history of the planet.