Deeper Layers Are Older

Rock layers are like pages in Earth's history book. Rock layers are bands of rock stacked on top of each other. Scientists study these layers to learn about the past. The key principle is simple: in undisturbed rock layers, deeper layers were laid down first and are older. The layers on top were added later and are younger.

Think of stacking pancakes on a plate. The pancake on the bottom was made first. Each new pancake you add goes on top. The pancake on the very top was made last. Rock layers form the same way. Over millions of years, sediment like sand, mud, and tiny pieces of rock settle on the ground or at the bottom of oceans. This sediment slowly hardens into rock. New layers keep forming on top of older layers.

This principle helps scientists determine the relative age of rocks and fossils. Relative age means which rocks or fossils are older or younger compared to each other, without knowing exact dates. Fossils are the remains or traces of plants and animals that lived long ago. If a fossil is found in a deep layer, it lived before a fossil found in a layer above it. By studying which layer a fossil is in, scientists can figure out the order in which different living things existed on Earth.

Interesting Fact: The oldest rocks ever found on Earth are about 4 billion years old! They were discovered in Canada and help scientists understand what our planet was like when it was very young.