“I am puzzled by signals from little green men” – Antony Hewish, 1967
Scientists have yet to verify any lifeforms originating on other planets, though there have been a few false alarms. Perhaps the earliest science had come to “detecting life” was in the late 1960’s. In 1967, Jocelyn Bell, was using a low-frequency radio telescope and noticed a distinct pattern of pulses that could not be attributed to man-made sources nor the quasars they were studying. Due to their perfectly timed nature, they seemed to have to come from life somewhere else.
Using a low-frequency radio telescope, built from wires strung between wooden poles, Jocelyn Bell, a student at the University of Cambridge, discovered pulses which were a third of a second long, with a pause of 1.3 seconds between. To Bell and her colleagues, the pulses were nothing like they had seen before. The project was named “Little Green Men” as an ode to the slight chance of contact from extraterrestrial life. 
As more signals were discovered, the frenzy among the inner team increased. The signals were coming from a body that may have been the size of a planet, relatively close to Earth, furthering the notion of extraterrestrial contact. Jocelyn and the team began debating if, and how, they would publish their reports, for the findings had no natural explanation. The implication would be phenomenal, that not only was life potentially out there, but that it was intelligent enough to send signals through the cosmos.
By February 1968, the frenzy had died down among the team. More sources for the pulses were found, showing that the signal was not a unique phenomenon, lessening the likelihood of extraterrestrials. The frequency of the wave and how it spread and decreased with speed pointed to natural sources, yet another reason to rule out other lifeforms. On February 8th, 1968, Jocelyn Bell and her team send a paper to a scientific journal, stating that the pulses, now named pulsars, were likely from a neutron star. 
The scientific community had been interested in looking for intelligent life for years, at that point, but had yet to find any evidence. While the pulsar was not a being from another world, the scientific community had a revitalization for searching for alien life. In 1974, Frank Drake began sending signals into the cosmos to begin communicating with other beings. 1976 brought the Viking Mission to the surface of Mars, where 3 of their tests found possible Martian life (while a gas chromatograph and mass spectrometer disputed those tests). In 1996, David McKay found what looked to be cellular structures on a meteorite from Mars. 
Even today, the search for life and habitable planets continues. Jocelyn Bell and her keen eyes not only discovered pulsars, but made the search for life outside our world an exciting renewed possibility.
 A. Penny, "The SETI Episode in the 1967 Discovery of Pulsars," European Physical Journal H, 2013.
 S. A. Benner, "Defining Life," Astrobology, pp. 1021-1030, 2010.
I liked that you had several examples and thought that you wrote in a clear and easy to follow way. I would have liked it if you elaborated more on the examples and how they supported your main point. Your post came off more as a summary than a discussion of an idea.
Very interesting post, I enjoyed it. You are extremely thorough on your references and it looks like you made quite some research. This to me, however, looks like a research paper instead of you sharing your opinion on these ideas. I would like to see your opinion and your take on these findings!