Allende is the most important and most thoroughly researched meteorite of all time. On 8 February 1969, just as geochemists around the world were fine-tuning their analytical equipment in preparation for the return of the first Apollo samples that July, a shower of meteoritic stones pelted a little village in Chihuahua, Mexico. The stones were gathered up by local residents who sold them to the hordes of scientists who had rushed in. Geochemical, petrological and isotopic analyses began almost immediately. Researchers found that the meteorites were all pieces of a single carbonaceous chondrite that had disintegrated high in the atmosphere. There are eight major groups of carbonaceous chondrites, each derived from a separate parent asteroid. The “CV” group, of which Allende is the most prominent member, possesses the largest (and most easily studied) chondrules and inclusions. Scientists quickly noticed the abundant large CAIs and found that they contained minerals that condensed at high temperatures from a cooling gas at the earliest stages of Solar-System history. In fact, these inclusions are the oldest rock samples in the Solar System, dating back 4.567 billion years.

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