Listen to David Monacchi's recordings of the oldest rainforests of the world. 

http://www.fragmentsofextinction.org/listen-to-ecosystems/

 

Bernie Krause has been recording wild soundscapes for 45 years. Here's a TED talk on his inspiring work. 

http://www.ted.com/talks/bernie_krause_the_voice_of_the_natural_world?language=en

And an article about disappearing soundscapes.

https://www.theguardian.com/environment/2012/sep/03/bernie-krause-natural-world-recordings