A special chemistry occurs at high altitude in planetary atmospheres. And this chemistry might have played a key role on the early Earth for prebiotic chemistry and the emergence of life.  
At high altitudes indeed, the molecules composing planetary atmospheres are submitted to the harsh radiation of the sun (or the host star for exoplanets). This leads to a chemical activation of all molecules, and even the most stable ones.
This original chemistry has been recently studied in depth on Titan, the largest satellite of Saturn, thanks to the amazing Cassini-Huygens space mission. So my talk will be largely based on Titan’s discoveries, but I will also address how far Titan chemistry can also be extended to the early Earth case and to rocky exoplanets outside our solar system.