As one of the world's most abundant and accessible renewable resources, wood has been of immense utility and value to humans. Wood can be durable (resistant to decay and insect attack) and long-lasting, and has often survived as fossil or archeological material; it is therefore one of the major sources of information on past vegetation, climate, and civilization. When wood is burned to form charcoal, the carbonized product is completely inert, but retains most of the anatomical characteristics of the original wood and can similarly be studied. Charcoal with good preservation is known from at least as far back as the Carboniferous Period, when conifers first appeared in the fossil record.