The Rise, Fall, and Rise of Fire

When I started my doctoral research in October 1973 I never imagined that I would spend so much of my career thinking about fire. I had not considered fire as an agent of change on Earth, or that charcoal deposits may preserve its long history on the planet. I had never thought of fire as a preservational mechanism for fossil plants, producing charcoal that would show their anatomy so that they could be identified, and help us to piece together the vegetation that must have clothed the land millions of years ago. In all my years of collecting fossils as a child and student I had never found, or at least noticed, any fossil charcoal. I had wanted to look at the ecology of the plants that were found during the Carboniferous, 300 million years ago. The natural approach was to look at the large fossil plants that could easily be found in rocks such as the Coal Measures that are often found scattered on old coal tips. But many smaller plant fragments are also preserved in the rocks. I started a programme of dissolving the rocks in acids and obtaining residues of the fossil plants that remained. The rocks are made up of minerals that dissolve in different acids from the plant fossils, which are made of organic material. It was hard work, and I spent many hours a day picking through the plant fragment residues, which were about the size of tea leaves, trying to identify what the fragments represented. Incredibly, at that time, few researchers had tried to look at plant fossils in this way. I soon noticed a large number of fragments that looked like charcoal, and examined these with an SEM. Under the SEM the astonishing detail in the charcoalified leaves was revealed (BW Plate 6). The small needle-like leaves had two beautifully preserved rows of stomata. But what kind of plant did they come from? I took the material to Bill Chaloner, who was one of the world’s authorities on the lycopods, one of the most common plants found in the coal measures.