I (artist first, and only an armchair scientist) know two things about the Carboniferous, the 60 million years between the Devonian and Permian.
First, there was an abundance of oxygen in Earth's atmosphere, which allowed insects, like the life-size dragonfly depicted here, to grow to enormous (scary!) size. Beautiful though!
Second - the lush forests in the upper panel, dying and sinking into the ground as all forests eventually do - were the birth of today's fossil fuel enterprise. Beds of coal, pools of petroleum, below.