Geologic eras are units of time into which the earth's history can be divided. Examples of geologic eras are the Paleozoic, then the Mesozoic and finally the Cenozoic. The Mesozoic is the geologic era in which dinosaurs lived on earth and can be divided into three stages: Triassic, Jurassic and Cretaceous. The period that does not belong to the Mesozoic Era is the Devonian, since it belongs to the Paleozoic Era.
She's trying to find the affect different shapes have on the distance the plane flies, not the affect different types of paper have on distance. If she were to use different paper for each plane she'd be testing two variables instead of one.
