The funding situation colors any discussion of SETI activities and timelines, Shostak said.
ANALYSIS: Why the Hunt for Extraterrestrial Life is Important
The 24-year estimate, for example, "depends on continued SETI funding, which is in dire straits right now," he told Space.com after his talk at the NIAC symposium.
A Three-Way Race to Find Life In Space The search for alien life does not focus solely on technological societies, of course. Many other scientists are keying in on simple life forms, which must be distributed much more commonly throughout the universe.
The first evidence of microbial life on Earth, for instance, dates from 3.8 billion years ago - just 700 million years after our planet formed. But it took another 1.7 billion years for multicellular life to evolve. Humans didn't emerge until 200,000 years ago, and we've become a truly technological species in just the last century or so.
Shostak thus views the alien life hunt as a three-way race. The contenders are researchers looking for advanced, intelligent civilizations; scientists scouring solar-system bodies such as Mars and Jupiter's moon Europa for simple organisms; and researchers focusing on finding signs of microbial life on nearby exoplanets using future instruments such as NASA's $8.8 billion James Webb Space Telescope, which is scheduled to launch in 2018.