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
What Is This? following week. The group decided to change their name to the Red Hot Chili Peppers, played several more shows at various L.A. clubs and musical venues, and eventually recorded a demo tape, all while Slovak and Irons were still playing with What Is This?. A few months later, What Is This received a record deal with MCA Records and the Red Hot Chili Peppers received a joint deal with EMI America and Enigma Records. Hillel Slovak and Jack Irons decided to leave the Red Hot Chili Peppers and stay with What Is This? as the latter was their primary musical