Why couldn't Earth have fire for billions of years?

The Earth is approximately 4.54 billion years old, but according to fossil evidence, fire only appeared a few hundred million years ago due to the right conditions.

Wildfires in Canada in June 2023. Photo: Reuters — Wildfires in Canada in June 2023. Photo: *Reuters*

Earth is the only known planet with fire. While volcanoes erupting hot magma may exist on the surface of Venus, the hottest planet in the solar system, fire has never been present there. Neither Mercury, Jupiter, nor any other planet in the solar system or other star systems has ever had fire.

In fact, for a long period in Earth's history, fire didn't exist. It took billions of years for conditions on the planet to become suitable for fire to appear. The first organisms on Earth lived in a fire-free world for longer than most people think. Volcanoes may create "flames" like those on Jupiter's moon Io, but these are magma forced up and erupting through vents, not actual fire.

Approximately 2.4 billion years ago, Earth's atmosphere was most likely a thick cloud of methane – the result of bacterial life forms appearing on the planet. Then, the Oxygen Catastrophe occurred, when ancient cyanobacteria began generating energy from sunlight, releasing oxygen into the atmosphere. Here, molecular oxygen began to accumulate in the atmosphere for the first time, though not yet at concentrations sufficient for combustion. The Oxygen Catastrophe, also known as the Great Oxidation Event, may have pushed Earth to a deep global freeze because this oxygen destabilized methane and caused a greenhouse effect collapse. Earth became frigid and fire ceased to exist.

For plant combustion to occur, the oxygen level in the atmosphere must be above 13%. However, if the oxygen level is higher than 35%, the fire will burn so intensely that the forest cannot grow and survive. Plants become increasingly flammable as oxygen levels increase, and 35% is the ceiling; exceeding this level will cause plant biomass to easily catch fire and burn so intensely that it becomes incompatible with the sustainable development of the forest.

Approximately 470 million years ago, during the Ordovician period, the first terrestrial plants—true mosses and filamentous mosses—produced more oxygen, eventually reaching concentrations sufficient to cause fires. Scientists obtained the first fossil evidence of fire on Earth: charcoal samples embedded in rocks dating back approximately 420 million years. However, with oxygen levels still fluctuating wildly, large-scale forest fires did not occur until around 383 million years ago. Since then, numerous intense forest fires have raged across the Earth.

Thu Thao (According to IFL Science )

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