A very interesting lecture from Geoff VK2TGO this month on what can be heard on the VLF band (below 22kHz, which is essentially the audio band except in RF!).  Sferics, Whistlers, the Dawn Chorus..  our planet makes a lot of noise!!

Unfortunately the video cut off at the 18 minute mark but it is a great subject worth sharing.

Watch the video here

Download the lecture slides here