The show’s latest episode harks back to a beloved episode that has had fans scratching their heads for 17 years.

Subscribe now to get unlimited access to TIME.com and more! TIME speaks with the winner of the XPrize Carbon Removal award, Mati Carbon, which was announced at the TIME100 Summit on April 23.

Welcome to Nat Geo Your Shot: National Geographic’s global community for aspiring visual storytellers. Find the community on Instagram @NatGeoYourShot and follow along for hashtag challenges ...