When plants die today, fungi decompose them, releasing their trapped solar energy. In the Carboniferous, most fungi apparently had not yet evolved the ability to break down lignin, the tough compound that gives plant stems their strength and bulk. Buried in almost oxygen-free sludge, attacked only slowly or not at all by fungi, the lepidodendrons, horsetails, and giant ferns decayed at an infinitesimal rate, creating layers of peat. Over the eons, crushed and heated by the slow churning of the earth, the peat became coal. All the while, in a parallel process, the earth was crushing and heating
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