This is clearly a meteorite that doesn't fit any of our previous classifications. Orgueil is the touchstone against which they compare the composition of the Earth, the moon and other celestial bodies. The Science study was led by the University of Western Ontario's Peter G. Brown. Clayton contributed the study's oxygen isotopic measurement, a key piece of data in revealing the meteorite's unusual composition.
Isotopes are the siblings of the elemental world.
They are atoms of an element that have different numbers of neutrons, and hence they have slightly different chemical properties. Oxygen has three isotopes, which Clayton uses to trace meteorites to their points of origin. One of Clayton's colleagues puts it another way. Broadly speaking, the Tagish Lake meteorite is a carbonaceous chondrite. This type of meteorite has changed little since the birth of the solar system approximately 4.5 billion years ago.