"Earth Quack" is the twenty-ninth episode of DuckTales. It is based on the Carl Barks comic story Land Beneath the Ground!.
One day Scrooge is in his Money Bin swimming around in his money, when suddenly an earthquake occurs. As if that wasn’t bad enough, the wall cracks open and his money falls right into the hands of a trio of giant-sized Beagle Boys.
Webby wakes up Scrooge, who had fallen asleep in his office, and was just having a nightmare. Or rather, a daymare, as it’s the middle of the day. Scrooge tells Huey, Dewey, Louie and Webby about how several earthquakes have occurred recently, and he fears that his money bin could be the next target. After doing some research, Gyro points out that the Fudderman Fault lies directly underneath the Money Bin, and that it’s overdue for another earthquake. Gyro recommends setting up a giant shock absorber in the fault in order to prevent any future earthquakes.
Later, at the outskirts of Duckburg, workers have already dug a hole leading deep underground. But suddenly, the workers flee the hole, claiming that they heard strange voices. Scrooge wants to get to the bottom of this (literally), so he heads down the hole in a mine cart. However, Scrooge goes down too far and loses contact with Gyro, so Huey, Dewey and Louie go after him in a second mine cart. Scrooge reaches the end of the track and crashes through the wall, revealing a secret path leading down even further, while the boys follow him. When Scrooge finally crashes, he gets knocked out just as a group of shadowy figures find him.
The boys manage to stop their cart just before it falls down a chasm, and experience an earthquake, along with whistling, so they go to check it out. Meanwhile, Scrooge is exploring on his own, when several balls of various colors begin to follow him. The balls reveal themselves to be Terra-Firmians; roundish creatures that can roll up into balls. They leave Scrooge, telling him that they're off to see the games. In a nearby cavern, a Terra-Firmian coach is ordering some other Terra-Firmians to practice for the games by rolling into a pillar simultaneously. It turns out that this rolling is what’s causing the earthquakes after all.
A blue Terra-Firmian boy wants to practice too once the others have left, but the coach tells him that he’s too small. The coach lets him try it once, but the kid is no good at it. The boys then crash their mine cart near where the coach and kid are, where they befriend the kid, who takes them to the games, where they hope Scrooge might be. As for Scrooge, he is with some other Terra-Firmians when their king shows up to officially open the Great Games. The king shows off a cracked vase, known as the Crack Pot, which is a trophy to the Terra-Firmians.
Before Scrooge can speak to the king, the Terra-Firmians begin with the opening roll, by rolling into a huge pillar. Scrooge tells them that their rolling is causing earthquakes, but the Terra-Firmians don’t seem to care. Scrooge makes a scene, and is taken to the Terra-Firmian jail. Huey, Dewey and Louie break open Scrooge’s cell by ramming a mine cart into it, freeing him. On their way back from the jail, Scrooge brings the mine cart with him, claiming that he’ll take the Crack Pot trophy just so that the Terra-Firmians will stop their games.
The kid shows up and tries to stop Scrooge and the boys, but gets knocked away, and ends up rolling into the giant pillar, receiving applause from the crowd. While riding the mine cart, Scrooge and the boys steal the Crack Pot and flee. They hide from the Terra-Firmians in a small cavern, and ride a geyser up to a higher level, but not without Scrooge losing his hat. Although they no longer have the Crack Pot, the king declares that Scrooge’s hat will be their new trophy.
Up on the surface, Mrs. Beakley suggests that she and the others should go down after Scrooge and the boys, just before the four ducks finally return. But the Terra-Firmians continue their game, triggering a huge tremor and causing an earthquake. Duckworth drives everyone to the Money Bin, which is where the earthquake is headed, but it’s hopeless. The earthquake cracks open the Money Bin, causing all of Scrooge’s cash to fall down into the caverns below. But the Terra-Firmians have no use for the money, so the king suggests that they play one more rolling game.
Scrooge’s friends and family lift his spirits, just as the Terra-Firmians roll into the huge pile of money, forcing it back up into the Money Bin and sealing the crack. Scrooge is thrilled to get his money back, and the Terra-Firmians are all proud of the kid. One of the king’s guards asks where the next Great Games will be held, and the king tells him that they’ll be out west somewhere, underneath a place called "Califermy".