Life expanded rapidly during the Cambrian period

By the early Cambrian period (543-490 mya), at the beginning of the Paleozoic era, the O2 concentration in the atmosphere approached its current level and the continental plates came together to form several land masses. The largest of the land masses was called Gondwana (Figure 22.9a). All of the major groups of animals that have species living today appeared during the Cambrian. This rapid diversification of life is referred to as the Cambrian explosion.

The most extensive fossil evidence from the Cambrian comes from the unusually well preserved animal fossils recently discovered in northeastern China (Figure 22.9b). Arthropods (crabs, shrimps and their relatives) are the most

22.8 Ediacaran Animals These fossils of soft-bodied invertebrates, excavated at Ediacara in southern Australia, formed 600 million years ago. They illustrate the diversity of life that evolved in Precambrian times.

Mawsonites

Spriggina floundersi

22.8 Ediacaran Animals These fossils of soft-bodied invertebrates, excavated at Ediacara in southern Australia, formed 600 million years ago. They illustrate the diversity of life that evolved in Precambrian times.

Mawsonites

Cambrian Period

Cambrian Ordovician

Silurian

Devonian

Carboniferous

Permian

Triassic

Jurassic

Cretaceous

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