Defining the Principle of Faunal Succession
The principle of faunal succession states that different fossil species appear and disappear in the rock record in a specific, reliable, and predictable order. Sedimentary rock strata in a given location contain fossils in a definite sequence, and this same sequence can be found in other locations, allowing for correlation between rock layers.
Section 2: How It Works
This principle is based on the fact that species evolve and go extinct over time. Each species existed for a specific period in Earth's history, and its fossils are confined to that time interval. Therefore, a rock layer containing fossils of a particular species can be identified and dated relative to other layers based on the known time range of that species.
Section 3: A Practical Example
Imagine a geologist finds a rock layer with trilobite fossils. In a layer above that, they find fossils of early dinosaurs. Far above that, they find fossils of mammoths. Because trilobites are known to be much older than dinosaurs, and dinosaurs are older than mammoths, the geologist can confirm the relative ages of these rock layers. The bottom layer is the oldest, and the top layer is the youngest.
Section 4: Importance in Geology
The principle of faunal succession is a cornerstone of relative dating and stratigraphy. It allows geologists to correlate rock layers across vast distances, even across continents. By matching the sequence of fossils, they can piece together a more complete geological history of Earth and create the geologic time scale.