The Pulse of Alien Life
Click to viewIt would be particularly exciting if combustion products -- those produced by ordinary fires, e.g., carbon monoxide, carbon particles (soot), etc. -- were found in the spectrum of an atmopsphere of a planet of roughly the size of Earth and located in its star's Goldilocks Zone, the range of distances from a star at which liquid water could exist on a rocky planet's surface. Combustion products in a planet's atmosphere would imply that it had an oxygen atmosphere and land-life that could provide fuel for fires caused by whatever source (lightning, anthropogenic, volcanic, etc.) -- water-life won't burn to any extent, simply because it's in water, and without oxygen, you can't have ordinary combustion. Land-life capable of providing fuel for fires would have to be something like Earth's vascular plants, which would mean at least fairly complex land-life. By itself, that would say nothing much about whether a technologically advanced civilization lived on that world, but it would say that perhaps one could, because conditions there would allow for it. And it would shout out that complex life is not unique to Earth.
One of these days we'll be able to capture the spectral signatures of the atmospheres of smaller worlds. When we do that, the hunt will be on for complex life on those worlds.