Choosing a Rock-History Display for the Polo Field

A Display beside the Polo Field

A polo club wants a history display beside its grassy playing field. Polo is a team sport played on horseback. Outside the playing area, a low rock ledge exposes layers beneath the field. The display will help visitors imagine what this place looked like long before people played sports here. Students compare two proposed display designs using photographs and a geologist’s records.

Geologist Dr. Okafor photographs the west and east ends of the ledge. Students work from her photographs rather than climbing on the rock. She checks that the layers are undisturbed: they have not been overturned or mixed. In each stack, a lower layer formed before the layer above it. A layer may become thicker or thinner along the ledge. Thickness alone does not reveal its age or how long it took to form.

Fossils are preserved remains or traces of ancient living things. Dr. Okafor identifies the fossils with a guide. The fish and snail kinds in these records lived in freshwater lakes. The coral kinds lived in shallow salt water. Rooted tree stumps show where trees grew on ground exposed to air. Dr. Okafor finds that the fossils were preserved where the organisms lived, rather than carried in from a different environment.

The records list the rock layers from top to bottom. The same kinds of fish and snails occur in more than one layer. To explain the history, students must consider what lies between those layers. No measurements give the ages in years. The present playing field is dry ground, but its grass and soil are not included in the ancient rock-layer records. A useful display should separate observations from ideas that still need evidence.