Principle of faunal succession facts for kids
The principle of faunal succession (also called the law of faunal succession) is a key idea in geology. It means that different layers of rock, called strata, contain different types of fossils. These fossils appear in a specific, reliable order from bottom to top. This order can be seen over large areas.
For example, you would never find a fossil from a Neanderthal (who lived less than 500,000 years ago) in the same rock layer as a Megalosaurus dinosaur (who lived about 160 million years ago). This is because these creatures lived during very different geological periods, separated by millions of years. This principle helps scientists figure out the age of rock layers by looking at the fossils inside them.
This important idea was named by an English geologist named William Smith. It helps scientists determine the relative age of rocks and their layers. When combined with the law of superposition (which says that in undisturbed rock layers, the oldest layers are usually at the bottom), it helps us understand the timeline of how sedimentary rocks were formed.
How Fossils Show Change Over Time
The idea of evolution helps explain why we see fossils change in this specific order. Older, simpler life forms are found in lower rock layers. As you move up through the layers, you find fossils of more modern and complex organisms.
William Smith first wrote about this in England in the early 1800s. Around the same time, Georges Cuvier and Alexandre Brongniart were studying similar patterns in France.
For instance, scientists studying how birds evolved predicted that early feathers would be found on creatures that couldn't fly, like feathered dinosaurs. And that's exactly what the fossil record shows! Simple feathers, not good for flying, are found in older layers. Then, in newer layers, we find fossils with larger and more complex feathers.
Using Fossils to Date Rocks
Scientists use special fossils called diagnostic species to help them date rocks. These are fossils from species that lived for a relatively short time but were found in many places. Studying these fossils to date rocks is called biostratigraphy.
In younger rock layers (from the Cenozoic Era), tiny fossils of creatures called foraminifera are often used. Each specific rock unit, called a biozone, is defined by the unique types of fossils it contains. This helps scientists create a very detailed timeline of Earth's history.
In simple terms, older fossils are usually simpler than newer ones. And newer fossils look more like living creatures we see today.
See also
- Index fossil
- Law of superposition
- Principle of cross-cutting relationships
- Principle of lateral continuity
- Principle of original horizontality
- History of paleontology
