23.1 Evolution refers to change through time
23.2 Chemical evolution
23.3 Evidence for evolution
23.4 The signs of evolution
23.5 Many factors contribute to evolution
23.6 The theory of evolution
23.7 Precambrian era
23.8 Gallery: Precambrian era
23.9 Paleozoic era
23.10 Gallery: Paleozoic era
23.11 Mesozoic era
23.12 Gallery: Mesozoic era
23.13 Cenozoic era
23.14 Gallery: Cenozoic era