Every Then & Theory plate comes from a true story, and this card tells the one behind yours.

The Then & Theory team

Reading the layers

This plate stacks history inside a letter, with fossils at the foot and a skyline at the top. Geologists read layers of rock from the bottom up. In 1669 the Danish scientist Nicolaus Steno, working in Tuscany, published the idea that layers of sediment settle one on another, so the lowest layer formed first. It is called the principle of superposition, and it let people put rocks in order long before anyone could give them an age in years. In 1666 Steno had dissected the head of a great white shark and drawn its teeth, which looked just like the “tongue stones” found in rock.

Note. Steno was not the first to match tongue stones to shark teeth, but his published drawings left little doubt.

Sources

1. NASA Earth Observatory, “Nicolaus Steno (1638–1686)”
2. Britannica, “Nicolaus Steno”