Hidden Layers by the Backyard Sundial

A Backyard Mystery

A sundial stands beside a low, natural rock face in Priya's backyard. Grass grows on the dry ground nearby. Part of the rock face is easy to see, but plants hide other parts. Priya wonders what photographs of the hidden rocks might show. Her aunt, a geologist, helps her science club study the exposed layers without digging or moving plants.

First, the club photographs the clearest section from level ground. Students do not climb or chip the rocks. The geologist checks that the layers have not been overturned or mixed. In this stack, a lower layer formed before a layer above it. Students label five layers, starting with layer 1 at the bottom and ending with layer 5 at the top.

Next, students examine close-up photographs. They record each layer's rock type, color, and fossils. The same layer can extend sideways through a rock face, although its thickness and fossils may vary. To predict what is hidden, the club will compare several clues rather than relying on a single fossil or rock color.

A reference card describes the identified fossil groups. The pondweed and mussel groups lived in freshwater ponds. The coral and sea urchin groups lived in salt water. Fossil stumps with roots still in their growing positions show where trees grew on land. The geologist checks the fossil identifications and confirms that the stumps and corals are preserved where they grew.

Finally, the club records the visible rocks near the sundial end of the face. Plants hide parts of this section. An adult will later provide clear photographs of those areas, taken before the plants covered them. The club will compare its predictions with those photographs. These records do not include ages in years. Decorative paving stones elsewhere in the yard were purchased and brought there.