Lighting a cigarette or a gas stove, making fire at picnic site, flaming fireworks at New Years’ Eve, or heating up the fireplace is easy nowadays. Mostly we need a matchstick or a lighter. A mix of antimony sulfide, potassium chlorate, gum, and starch were all that was required to prototype a matchstick in 19. century. Around the same time was also the lighter invented.
Fire, as we know it, is a chemical reaction called combustion that has three ingredients: a fuel (i.e. gasoline, wood), oxidizing agent (i.e. oxygen in the air), and heat. The combustion releases energy in the form of light and heat, and we call it flames.
It is mesmerizing that the Earth is the only planet where fire, as an output of combustion, can exist. Earth is uniquely suited for fire as we know it because it has an atmosphere that contains about 21% oxygen and supports a wide range of temperatures in which fire can occur.
The other planets in our solar system do not have the necessary conditions for Earth-like fire to exist. For instance, Mercury has no atmosphere, so no oxygen. Venus has an atmosphere, but made of almost only carbon dioxide. Jupiter, Saturn, Uranus, and Neptune are gas giants with no solid surface and atmospheres composed mainly of hydrogen and helium.
For most of Earth’s history, there was no enough oxygen to support the combustion, thus the fire. The event that changed everything was the Great Oxygenation Event, which occurred around 2.4 billion years ago when cyanobacteria in Earth’s oceans began producing oxygen through photosynthesis. However, it wasn’t until roughly 400 million years ago that land plants proliferated and significantly increased oxygen production, raising atmospheric oxygen levels to the point where fires could occur more widely.
Considering that the universe is about 13.8 billion years old, if you were to scale this down to a single year (the Cosmic Calendar), enough oxygen was available for fire to burn only in the last 10 days of that year. This puts into perspective how recent the phenomenon of fire is on the cosmic scale and highlights Earth’s unique conditions that make fire possible.
As we gather around our campfires, or watch as wildfires are battled, it’s worth a pause to consider this extraordinary phenomenon. Fire has been a cornerstone of human civilization, a tool that has cooked our food, forged our metals, powered our engines, and powered guns that killed many people. As we start to explore the cosmos, we should keep in mind that this vibrant flame is, for now, an Earthly privilege—a precious anomaly in the silent expanse of the universe.