Definition

The fossil record is all the fossils that have ever been found, arranged from oldest to youngest, like a giant picture book showing what lived on Earth at different times. It is the ordered sequence of fossils preserved in Earth's rock layers, and because deeper layers are older, it shows the succession of life through time: simple marine organisms first, then more complex forms. It provides evidence for evolution, extinction, and changing environments and climates, though it is incomplete because fossilization is rare. The record documents the principle of faunal succession, the basis for biostratigraphy, and reveals large-scale patterns: the Cambrian explosion of animal body plans about $539$ million years ago, five major mass extinctions, and adaptive radiations that followed each. Statistical analysis corrects for sampling bias, rock volume, and preservation potential. Transitional fossils such as Tiktaalik (fish to tetrapod) and feathered dinosaurs link major groups.