How do they reason? Fire. Fire transformed human technology, from forging metals to powering engines. But fire needs oxygen, lots of oxygen. They estimate that an exoplanet’s atmosphere must contain at least 18% oxygen (this level is called the “oxygen bottleneck”) to support the controlled use of fire.
This does not mean that life cannot exist below this threshold. Bacteria can thrive in a low-oxygen atmosphere, but creating the building blocks of advanced technology will be a major hurdle. Imagine trying to build a rocket without melting metal or producing excessive heat.
So why focus on oxygen when other molecules such as carbon dioxide are already being studied? Because it is easier to detect oxygen in the atmospheres of distant exoplanets. Although phosphorus points to the possibility of life, it does not tell us how advanced life might be.
This approach to searching for alien civilizations using “techno-signatures” is still in its infancy, but the idea of using oxygen as a filter adds an important new dimension to the search.
Source: Ferra
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