When Ronnie's parents go on a business trip and leave her with Miss Lernin for the week, Ronnie is sure she's in for a big, dinosaur-size adventure. So, when they end up at the aquarium's jellyfish exhibit, Ronnie is confused. Surely jellyfish aren't as cool as dinosaurs, right? Wrong! Determined to show Ronnie just how interesting prehistoric life was before the age of the dinosaurs, Miss Lernin takes her back in time to the six parts of the Paleozoic era to study the earliest lifeforms on Earth, and how many left the ocean for life on land.