化石记录

The dinosaur Triceratops ate plants and stood approximately 8 feet tall. Scientists inferred its shape, size, and behavior from fossils, preserved remains or imprints, such as footprints, bones, and teeth.

Most organisms do not fossilize after death. Decomposers, such as bacteria and fungi,  and scavengers, such as flies and beetles, typically destroy tissues before fossilization can occur. Soft tissues, such as muscles, feathers, and fur, often disappear, while hard tissues—including bones, teeth, and shells—more commonly remain.

Fossils, like a mammoth encased in ice or a spider preserved in amber, offer an extremely rare glimpse of intact, early life-forms.

Sedimentary rocks yield the most fossils, particularly as fragments rather than complete organisms.

Sedimentary fossils form when sediment, such as sand or mud, buries an organism or its tracks. Pressure and heat transform the layers into rock, creating a fossil. These sedimentary rock layers, or strata, accumulate fossils over time.

Stratigraphy—the study of strata deposited through time and space—allows scientists to determine the relative age of fossils.

For example, strata form horizontally, with newer layers forming abov