Scanning electron microscope studies of particulate matter in Cretaceous/Tertiary boundary sediments reveal no common carrier phase larger than about 1 μ m for the supposedly extraterrestrial elements. Particles possibly related to an extraterrestrial impact are Fe-rich aluminosilicate spheres (similar to microtektites), Al-rich smooth spheres, K-rich feldspar spheroids, and Fe-Ti–rich particles. Mercury abundances in bulk sediment samples show no consistent enrichment pattern. Some of the supposedly extraterrestrial elements (e.g., Pt, Ni) are present within diagenetic sulfide grains. Terrestrial processes have modified the extraterrestrial element signature, and characterization of an impactor simply from sediment chemistry is erroneous. Deep-sea sediments not enriched in chalcophiles will probably provide the best clues for impactor identification.