Fossil record of fire

A modern-day wildfire

The fossil record of fire first appears about 430 million years ago during the Silurian period, with the find of charcoal in Silurian layers of Wales and Poland, which is an esteemed proof that fires happened to the then-existing macroscopic land plants.

To occur, fire needs oxygen in the air. In the oceans of the Proterozoic eon, the rise of eukaryotic photoautotrophs (green and red algae) for hundreds of millions of years injected further oxygenation into the air and, much later, the appearance of macroscopic land plants (embryophytes) led to increased levels of oxygen in the atmosphere as the new hordes of land plants pumped it out as a waste product. When this concentration rose above 13%, it led to the possibility of wildfire. Wildfires were first recorded in the late Silurian fossil record, 430 million years ago, evidenced by fossils of charcoalified plants found in the 2020s. Before these finds, evidences of wildfires dated 420 million years ago had been found in the early 2000s. Apart from a controversial gap in the Late Devonian, charcoal has been present in the fossil record ever since then. The level of atmospheric oxygen is closely related to the prevalence of charcoal, as oxygen is the key factor in the abundance of wildfire. Fire also became more abundant when grasses became the dominant component of many ecosystems, around 6 to 7 million years ago; this kindling provided tinder which allowed for the more rapid spread of fire. These widespread fires may have initiated a positive feedback process, whereby they produced a warmer, drier climate more conducive to fire.