Oil shale is a term for oil trapped in rock, rather than existing in liquid form. Check out this HowStuffWorks podcast to learn more about the nature of oil shale.
Learn more about your ad-choices at https://www.iheartpodcastnetwork.com

Selects: Mangroves: Nature's Best Tree?
44:31

How the Kowloon Walled City Worked
41:27

Short Stuff: In-Flight Entertainment
12:23