Cambrian explosion
A geologically rapid diversification of animal life about 539–520 million years ago, when many major animal groups first appear in the fossil record.
Ediacaran–Cambrian transition: The interval spanning the end of the Ediacaran Period and beginning of the Cambrian Period, marked by major biological and environmental changes. This transition frames the environmental shifts associated with the diversification.
Burgess Shale: A middle Cambrian fossil deposit in British Columbia, Canada, known for exceptionally preserved soft-bodied organisms. Its fossils preserve an unusually broad array of Cambrian animal anatomies.
Charles Darwin: An English naturalist whose theory of evolution by natural selection was published in On the Origin of Species in 1859. Darwin recognized the sudden appearance of animal fossils as a challenge for his theory.
Ediacaran biota: A group of mostly soft-bodied organisms known from fossils dating to the Ediacaran Period, before the Cambrian. These older organisms show that complex life preceded the Cambrian diversification.
Cambrian substrate revolution: A shift in seafloor ecology as animals increasingly burrowed, grazed, and disturbed marine sediments during the Cambrian. Animal activity transformed seafloor habitats as diversification proceeded.
Oxygenation of the oceans: An increase in dissolved oxygen in seawater, which affects animal metabolism and marine ecosystems. Higher oxygen availability may have expanded the range of animal body sizes and lifestyles.
Chengjiang biota: An early Cambrian fossil assemblage in Yunnan, China, with exceptional preservation of soft-bodied animals. It records diverse animals near the early part of the diversification.
On the Origin of Species: Charles Darwin's 1859 book presenting evolution by natural selection and evidence for common descent. Darwin discussed the early fossil record as an apparent difficulty for gradual evolution.
Great Ordovician Biodiversification Event: A major rise in marine biodiversity during the Ordovician Period, after the Cambrian. It was a later expansion of animal diversity, not the initial appearance of many major groups.
Cambrian explosion and evolutionary theory: The use of the Cambrian fossil record to examine the pace, pattern, and mechanisms of evolution. The event tests how rapid diversification fits with evolutionary change over deep time.