VMBO Year 3 · Classification · Section 4.1

The history of life on Earth

How did life begin on Earth?

Earth formed approximately 4,600 million years ago. At first its surface was extremely hot. After it cooled and oceans formed, life emerged. There is clear fossil evidence of life from about 3,500 million years ago, with possible evidence from earlier dates. The earliest organisms were single-celled and lacked a nucleus. Later, photosynthetic organisms released oxygen, gradually changing the oceans and atmosphere.

From water to land

Multicellular life developed long before animals became common. By around 600 million years ago, early animals were present in the oceans. Around 540 million years ago, many animal groups diversified during the Cambrian period. Early vertebrates included fish. Plants colonised land roughly 470 million years ago, followed by different groups of land animals. Amphibian ancestors and later reptile ancestors evolved over subsequent millions of years; these groups did not all appear at the same time.

Dinosaurs and extinction

Dinosaurs appeared during the Triassic period, roughly 245–230 million years ago. They became a dominant group of land animals. About 66 million years ago, an asteroid impact caused severe environmental changes and a mass extinction. All non-bird dinosaurs disappeared. Birds survived and are the living descendants of one dinosaur lineage.

The emergence of humans

Mammals and birds existed before this extinction, but many groups diversified afterwards. The human lineage separated from the lineage leading to chimpanzees and bonobos roughly 6–7 million years ago. The genus Homo appeared much later. Our species, Homo sapiens, evolved in Africa; fossils date back around 300,000 years. Modern humans share ancestry, but our origins cannot be reduced to a single person living 150,000 years ago.

The tree of life

Throughout Earth's history, species have arisen, changed and become extinct. Organisms sharing a common ancestor are related. The more recent that common ancestor, the closer their relationship. An evolutionary tree shows these branching relationships, while a timeline places major events in chronological order.