Is atmospheric oxygen (and fire) a necessity for the rise of technological civilizations?
The use of fire by our ancestors nearly 2 million years ago paved the way for our evolution. But how crucial is fire for the rise of civilizations? A recent study uncovers the intriguing relationship between atmospheric oxygen and the possibility of fire-wielding civilizations on other planets. This leads us to the question; Is atmospheric oxygen (and fire) a necessity for the rise of technological civilizations?
Homo Ignus – The Fire-Wielding Ape
Nearly 2 million years in the past, Homo erectus, our upright ape ancestors, began to harness the power of fire. Transitioning from opportunistic users of natural fires to masters of flame creation, they laid the groundwork for human evolution. We’ve become creatures defined by fire, relying on it for cooking, warmth, and light. But it leads us to ponder: Could civilization have risen without fire?
The existence of fire is tied to the presence of oxygen in the atmosphere. An open flame requires an atmosphere with at least 18% oxygen content; 20% might be necessary for reliable ignition. Our current atmosphere consists of 21% oxygen, but it remained above 18% only for the past 200 million years. Thus, for most of Earth’s history, fire was unattainable. It highlights that planets supporting fire might be rare in the universe, potentially limiting the rise of civilizations elsewhere.
A Recent Study Sheds Light on the Bottleneck
A recent study published on the pre-print server Arxiv delves into the conditions required for an oxygen-rich atmosphere, revealing that they are remarkably specific. Two main methods can create free oxygen: biologically through photosynthesis and abiotically, where ultraviolet light splits water vapor into hydrogen and oxygen.
The study underscores that the prevalent mechanism depends on a planet’s size and temperature. On Earth, free oxygen needs living organisms. A planet that’s too small lacks sufficient atmosphere for life, and if too large, its atmosphere, dominated by hydrogen and helium, cannot produce enough oxygen to cross the 18% threshold. Consequently, inhabitants of a super-Earth with Earth-like temperatures may not have access to open flames.
The Case of Hotter Planets
For warmer planets, the abiotic process becomes dominant but only if the planet is larger than Earth. Smaller hot planets, like Venus, fail to produce a thick enough water vapor layer to generate significant oxygen. If we discover super-Earths with a rich oxygen atmosphere, it probably arose by abiotic means, potentially allowing life forms to harness that oxygen, even for fire-based civilization.
The paper doesn’t delve into every detail of atmospheric oxygen but aims to sketch the constraints for the creation of fire on possibly habitable worlds. As we explore the cosmos for signs of life, we may have to differentiate between worlds supporting life and those nurturing civilizations.
A More Rare Phenomenon Than Once Thought
The connection between oxygen-rich atmospheres, the possibility of fire, and the rise of civilizations sheds a new light on our understanding of habitable planets. The conditions for an oxygen-rich atmosphere are more stringent than previously believed, indicating that fire-wielding civilizations might be far rarer in the universe than we once hoped.
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