An earliest Triassic methane postapocalyptic greenhouse following the Permian-Triassic (P-T) extinction event was proposed on the basis of evidence of deeply weathered paleosols at high latitudes with features of low-latitude soils, and low stomatal index values of seed fern leaves. Reexamination of distinctive phyllosilicates, unique to a single stratigraphic level, in paleosols located just above the isotopically defined Permian-Triassic boundary in Australia and Antarctica furnishes additional tests of this hypothesis. Illite is the dominant clay mineral in earliest Triassic paleosols from Antarctica, but the paleosols also contain conspicuous green nodules of coarsely crystalline berthierine. Examples from the geologic record and from experimental studies indicate that the formation of berthierine is restricted to reducing conditions. The occurrence of this unusual mineral in soils may indicate soil oxygen consumption by the influx of atmospheric methane to form carbon dioxide, which in turn warmed the earliest Triassic, giving rise to a postapocalyptic greenhouse.