Cambrian period

The Cambrian period, approximately 541 to 485 million years ago, marks an important chapter in Earth's history when most major animal groups first appeared. During this time, life was mostly simple and aquatic, but it rapidly diversified into a wide variety of complex organisms, including early ancestors of many modern animals. This period is known for the "Cambrian Explosion," a relatively brief event where evolutionary activity greatly increased, leading to the development of shells, exoskeletons, and more complex body structures. It laid the foundation for the complex ecosystems we see today.