https://www.youtube.com/watch?v=5ovcD2uL5Cc

People are always worried that alien civilizations will detect the transmissions from our old radio shows and television broadcasts, and send in the invasion fleet. But the reality is that life itself has been broadcasting the existence of life on Earth for 500 million years.

Blame it on the plants.

In addition to filling the atmosphere with oxygen, plants give off a very specific wavelength visible in infrared radiation. It’s the kind of signal that other civilizations could search for as they’re scanning the galaxy.

 

Information on ESA's ARIEL mission:

https://www.youtube.com/watch?v=uCTGI...

 

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