We are taught fire needs three things (the combustion triangle): heat, oxygen and fuel. Watching a candle got me thinking about whether fire could exist without life.
A heat source may come from many places, the most likely natural one being lightning, but direct sunlight may also start a fire. Neither of these require the existence of life, so this would not be a problem if it did not exist.
Oxygen existed only in very small quantities until organisms began photosynthesising (possibly as early as 3.5 billion years ago). It is believed tiny amounts of oxygen were produced through water decomposing in the very upper atmosphere, as the hydrogen would escape into space, leaving the oxygen. However, it is unlikely this would even make up 1% of the atmosphere, let alone the 12% needed in the air to start a fire. On a side note, it is believed that without life, the atmosphere would be mostly made up of carbon dioxide and water vapour (percentages would depend on the Earth's temperature).
Were enough oxygen somehow able to accumulate without life, fire still would not be possible, as, as far as I'm aware, any form of fuel on earth is either alive, has once been alive, or has been modified by humans from something that once was alive.
Emily Lauterpacht
Agree as some substance with no life can be fired.
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