The windows of SETI--frequency and time in the search for extraterrestrial intelligence.
On Earth intelligent life evolved as a natural consequence of the events set in motion when the planet formed over 4 billion years ago.  Since chemical evolution and solar-system formation appear to be occurring throughout the universe, we theorize that our universe may be rich with planets populated by intelligent beings who, like us, can search for evidence of other technological civilizations.  Terrestrial civilization now has this capability.  But if we do not begin the search soon, we'll lose the opportunity to do it from Earth as interfering signals of Earthly origin rapidly close the microwave window.
Oliver
B M
BM
NASA SETI Program, USA.
D055580:Astronomical Phenomena; D001256:Astronomy; D003142:Communication; D018534:Earth, Planet; D018559:Exobiology; D005118:Extraterrestrial Environment; D008872:Microwaves; D000069497:Origin of Life; D016082:Solar System; D013997:Time Factors; D014481:United States; D018557:United States National Aeronautics and Space Administration