Aeronian

The Aeronian was a time period in Earth's history, part of the early Silurian Period. It began about 440.5 million years ago and ended about 438.6 million years ago. During this time, many important changes happened in the world's oceans and to the animals that lived there.

One major event during the Aeronian was called the Sedgwickii Event. This event caused a big drop in the number of different types of graptolites, which were simple sea creatures with long, thin bodies. Scientists have found evidence of this event in places that are now Canada, Libya, and in a rock layer called the La Chilca Formation in Argentina.

This was also the time when the first gnathostomes appeared. Gnathostomes were early fish that had real jaws, a big step forward in animal evolution. Two of the earliest known gnathostome genera were Qianodus and Fanjingshania.

GSSP

The Global Boundary Stratotype Section and Point (GSSP) for the Aeronian is near a farm in Wales, UK. It is in old, layered rock called mudstone. This rock has many tiny, ancient sea creatures. The rocks also have graptolites, which are small, ribbon-like fossils. These help scientists learn about different layers of Earth’s history.