Our Environment Contents

1. Evolution

Increases in oxygen allowed an explosion of skeletal life forms on Earth.

Trilobite fossils

Oxygen is a vital ingredient in the chemical reactions which are needed to produce skeletons from calcium and silica. Skeletons are important both for body structure and for protection. A substantial increase in the level of oxygen in the atmosphere created the conditions for the most spectacular explosion of life the Earth's history has ever seen - the Cambrian Event.

The Cambrian period stretched approximately from 570 to 500 million years before present. The Cambrian Explosion - a rapid diversification of multi-cellular organisms - is thought to have occurred 530 million years ago. Most of the phyla known today appeared in the first few million years or of the Cambrian period.

Trilobites are the most common Cambrian fossils. Trilobites (now extinct) were marine arthropods. Their hard outer skeleton allowed them to evolve into many different forms and to exploit many different lifestyles. Some were swimmers and predators, others burrowed into sediment and fed on mud.

Why is the skeleton important?