Coal the heat and pressure of deep burial causes the loss of water, methane and carbon dioxide and an increase in the proportion of carbon. Thus first lignite (also called "brown coal"), then sub-bituminous coal, bituminous coal, and lastly anthracite (also called "hard coal" or "black coal") may be formed. The wide, shallow seas of the Carboniferous Period provided ideal conditions for coal formation, although coal is known from most geological periods. The exception is the coal gap in the Permian–Triassic extinction event, where coal is rare. Coal is known from Precambrian strata, which predate land plants—this coal is presumed to
A Star Is Burns launch "The Critic" on Fox, and he thought having a film festival in Springfield would be a good way to introduce Sherman. After Brooks pitched the episode, the script was written by Ken Keeler. Although David Mirkin was executive producer for most of the sixth season, the episode was executive produced by Al Jean and Mike Reiss. Jay Sherman's appearance was Simpsonized: he was made yellow and given an overbite. The episode contains a meta-reference to the fact that it is a crossover episode in a conversation Bart has with Sherman: The joke was pitched by Al Jean. Alongside Jon