If the nearest civilization is 100 light-years away, we would have to sit around for 200 years for a reply to a deliberate broadcast. Nonetheless, a few, mostly symbolic, intentional messages have been sent. One message, transmitted in 1974 from the Arecibo Observatory, was a simple picture describing our solar system, the compounds important for life, the structure of the DNA molecule, and the form of a human being. The message was transmitted in the direction of the globular star cluster M13, about 25,000 light years away. All life on Earth is carbon based.
Carbon makes long chains with hydrogen, oxygen, and nitrogen.
Gunter Wachtershauser and Claudia Huber, German chemists, combined chemicals that exist where molten lava boils up through fissures. Medium was a reproduction of deep-sea vents. You have to realize that people in the origin of life field are not very straight. This is pseud-religious field. People behave like Grand Inquisitors.