Do technological civilizations depend on atmospheric oxygen?

Practically 2 million years in the past a species of upright apes generally known as Homo erectus started to make use of fireplace. It was a gradual course of, from opportunistic customers of pure fires to masters in a position to craft flames from flint and tender. We’re their descendants. We’re creatures of forge and kiln, fireplace and residential. Fireplace has change into so central to us that as a substitute of homo sapiens, we might name ourselves homo ignus, the fire-wielding ape. Fireplace is central to the rise of our civilization. It cooks our meals, retains us heat, and illuminates our evening. This raises an attention-grabbing query. May we now have constructed a civilization with out fireplace?

Fireplace is barely potential in an environment with a excessive oxygen content material. In atmospheres with lower than about 18% oxygen, you may’t have an open flame. Dependable ignition might require a stage as excessive as 20%. Earth’s ambiance is presently 21% oxygen however has been steadily above 18% for less than about 200 million years. For a lot of Earth’s historical past, open flames weren’t potential. And Earth is the one planet in our solar system with a big oxygen stage. So whereas planets are frequent within the universe, planets the place fire is feasible could possibly be uncommon. If civilizations want fireplace to come up, atmospheric oxygen could possibly be the bottleneck.

That bottleneck is the main target of a current research printed on the pre-print server Arxiv. It appears to be like on the necessities for a planet to have an oxygen-rich ambiance and finds the constraints are fairly stringent. There are solely two major methods to create free oxygen in an environment. The primary is the organic origin, the place dwelling organisms produce oxygen by means of photosynthesis. The second is an abiotic course of the place water vapor within the upper atmosphere is break up into hydrogen and oxygen by ultraviolet gentle.

The research exhibits that the dominant mechanism depends upon the scale and temperature of a planet. At Earth temperatures, free oxygen requires dwelling organisms. But when the planet is simply too small it will possibly’t maintain a ample ambiance for all times, and if it is too giant its ambiance might be so dominated by hydrogen and helium dwelling issues cannot produce sufficient oxygen to interrupt the 18% threshold. So residents of an Earth-temperature super-Earth most likely cannot have open flames.

For warmer planets, the abiotic mechanism dominates, however provided that the planet is bigger than Earth. Small sizzling planets will not have a thick sufficient water vapor to generate plenty of oxygen. Venus is an efficient instance of this, the place it’s too heat for biotic oxygen, however not giant sufficient for abiotic oxygen. This implies if we discover super-Earths with a wealthy oxygen ambiance, then it doubtless arose by abiotic means. It might nonetheless be potential for dwelling issues to make the most of that oxygen, together with utilizing fireplace to create a civilization.

The problem of atmospheric oxygen is advanced, and this paper would not go into the true particulars. Its goal is to stipulate the constraints on the power to create fireplace on doubtlessly liveable worlds. As we search for life within the heavens, we would want to tell apart between doubtlessly liveable worlds and doubtlessly civilized worlds.

The latter could also be rather more uncommon than we had as soon as hoped.