organic matter in comets

Comets contain a rich variety of organic materials, together with frozen gases, and refractory grains. Preliminary analysis of the samples of comet Wild 2 returned to Earth by the Stardust probe, for example, revealed that about 10% of the comet is made of organic matter. Since substantial amounts of cometary dust arrived on Earth shortly after our planet formed, it is at least possible that cometary material could have played a significant role in prebiotic processes prior to the appearance of microorganisms.