Cambrian Series 2

The Cambrian Series 2, also called the Mid-Early Cambrian, is an important time in Earth's history. It is the second major part of the Cambrian era. It sits above the Terreneuvian series and below the Miaolingian series.

Scientists have not yet officially defined this series. This means we do not have a clear starting point or exact way to divide it into smaller parts.

One way scientists think about the start of Cambrian Series 2 is by looking for the first appearance of a group of ancient sea creatures called trilobites. These small, multi-legged animals were some of the first complex life forms in the oceans. The appearance of trilobites happened around 521 million years ago, marking a key moment in the early Cambrian world. This time period helps us understand how life on Earth began to grow and change in ancient seas.

Naming

The International Commission on Stratigraphy has not yet given an official name to the 2nd series of the Cambrian period. When it is named, it will replace older terms like "Lower Cambrian" and "Early Cambrian". In some places, such as Siberia, this time is called the "Yakutian".

Subdivisions

The 2nd series of the Cambrian period has two main stages: Cambrian Stage 3 and Cambrian Stage 4. These stages are still being studied by scientists. In Siberia, three stages are used: Atdabanian, Botomian, and Toyonian. Most ways to divide this series look at fossils, especially trilobite zones.

In Australia, there is a stage called the Ordian. It was thought to be the first stage of the Miaolingian, but it might be part of the upper part of Series 2. As of 2024, the start of the Ordian stage has not been officially defined yet.

Biostratigraphy

The beginning of the second series of the Cambrian period is identified by the first appearance of trilobites. This helps scientists study and compare rock layers across different continents. The oldest known trilobite, Lemdadella, signals the start of the Fallotaspis zone.

The end of this series is marked by a big loss of marine life, known as the first major extinction of the Paleozoic era. Changes in ocean chemistry and marine conditions are believed to be the main reasons for this extinction. Many trilobite families disappeared, including Olenellidae in Laurentia and Redlichiidae in South China. After this extinction, new trilobites such as O. indicus appeared. Where their fossils are not found, scientists use chemostratigraphic data to identify the boundary.