Wood that refused to rot for 60 million years

During the Carboniferous period, trees evolved a new structural material called lignin. It made them strong and tall, but it had one major flaw: for a long time, scientists thought fungi couldn't break down lignin yet, but we now know that high water levels in swamps likely played a bigger role in stopping decay. When a tree died, it often just sat there, remarkably preserved, for centuries.

These dead forests piled up in massive heaps, dozens of feet thick. Because the wood wouldn't rot, the carbon inside it remained trapped instead of being released back into the atmosphere as CO2. This created an oxygen spike so massive that dragonflies grew to the size of seagulls and millipedes reached over eight feet long.

This era of 'immortal' wood eventually ended when a specific type of fungus finally figured out how to digest lignin. This massive carbon storage led to a period of global cooling and a significant drop in atmospheric CO2.

All those unrotted trees were eventually buried under sediment and cooked by the Earth's internal heat. Today, we dig them up and burn them for fuel. Roughly 90% of the coal we use today comes from that single 60-million-year window when the planet forgot how to decompose wood.