Petroleum-the transmuted fossils of ocean algae-forms when the rock that holds the fossils becomes heated to the temperature of a cup of coffee and remains as warm or warmer for at least a million years. The minimal temperature is about fifty degrees Celsius. At lower temperatures, the algal remains will not tum into oil. At temperatures hotter than a hundred and fifty degrees, any oil or potential oil within the rock is destroyed. (“The stuff is there, throughout the Appalachians. You look at the rocks and you see all this dead oil.”) The narrow “petroleum window,” as it is called-between fifty degrees and a hundred and fifty degrees-is scarcely a fourteenth part of the full temperature variation of the crust of the earth, a fact flexplek huren breda that goes a long way toward explaining how the human race could have used up such a large part of the world’s petroleum in one century. Not only must the marine algae have been buried for adequate time at depths where temperatures hover in the window but once oil has formed it is subject to destruction underground if for one reason or another the temperature of its host rock rises. Natural gas is to oil as politicians are to statesmen. Any organic material whatsoever will form natural gas, and will form it rapidly, at earth-surface temperatures and on up to many hundreds of degrees. In Anita’s words: “You get natural gas as soon as anything drops dead. For oil, the requisites are the organic material and the thermal window. When they look for oil, they don’t know what they’ve got until they drill a hole.” In trying to figure out where to drill, geologists have an obvious flexplek huren amersfoort need for geothermometers. Pollen and spores are of considerable use, but only when they have fossilized in certain rocks. Moreover, they are absent altogether from early Paleozoic times, and they are extremely rare in rock from the deep sea. Leonard Harris asked Anita how many years she had been “sitting on” her discovery about conodonts.