Choosing a Rock-History Panel at the Recycling Center

The Rock Record Beneath the Recycling Center

Before building a new sorting building, the recycling center hired a geology team to study two undisturbed cuts in the ground. The cuts were at the North Pad and the South Pad. The team recorded layers from the bottom upward. In an undisturbed stack, a lower layer formed before a layer above it. The layers do not have to be the same thickness to have formed at the same time.

The North Pad record was: N1, sandstone with fossils of shells from a shallow sea; N2, mudstone with fossil tree stumps and root traces; N3, limestone with freshwater snails and water-lily fossils; N4, sandstone containing many rounded pebbles but no fossils; and N5, mudstone with the same kind of shallow-sea shell fossils found in N1. The team identified the shell fossils as marine fossils and the snails and water lilies as freshwater clues.

The South Pad record was shorter: S1, sandstone with shallow-sea shell fossils; S2, mudstone with tree roots; S3, limestone with freshwater snails; and S4, mudstone with shallow-sea shell fossils. The South Pad layers were also undisturbed. The matching fossil groups and the order of the layers helped the team compare the two records, even though the rock names and thicknesses were not identical in every layer.

The center's education team tested two panel designs. Panel A showed the oldest layers at the bottom, labeled the fossil clues, and used arrows to show environmental changes. Panel B showed the center as dry land in each scene because the ground is dry today. The team needed to choose the panel that the rock evidence could support.