Related by context. Frequent words. (Click for all words.) 69 Cretaceous Period 63 Late Cretaceous 60 interglacial period 57 glaciation 56 interglacial 56 Pleistocene 56 Eocene 55 Pliocene 54 Holocene 54 Younger Dryas 54 Paleocene 53 tropics 53 temperate zones 53 Fertile Crescent 53 Homo sapiens 52 Ice Age 52 Cretaceous 52 Ardipithecus 52 Little Ice Age 52 Weddell Sea 52 marine sediments 52 Australopithecus 52 terrestrial ecosystems 51 subtropical regions 51 trilobites 51 African savanna 51 Oligocene 51 Carboniferous 51 Ordovician 51 landmasses 51 marine reptiles 51 equatorial 51 vertebrate species 50 Mesozoic 50 Australopithecus afarensis 50 multicellular 50 megafauna 50 fossil 50 temperate regions 50 dinosaurs roamed 49 hominids 49 multicellular organisms 49 biodiversity hotspots 49 Quaternary 49 Triassic 49 anatomically modern 49 diatom 49 biome 48 Medieval Warm Period 48 volcanic islands 48 archaea 48 species 48 Great Rift Valley 48 atmospheric CO 48 mass extinctions 48 single celled 48 tropical forest 48 amphibian species 48 tropical rainforests 48 volcanism 48 crocodilians 48 fossilized remains 47 CO2 concentrations 47 mass extinction 47 Galápagos 47 tropical rainforest 47 Homo habilis 47 equatorial Pacific Ocean 47 taxa 47 mid latitudes 47 Neandertal 47 atmospheric CO2 47 Gondwana 47 atmospheric carbon dioxide 47 mammals 47 Jurassic 47 Neandertals 47 genus Homo 46 equatorial regions 46 glacial melt 46 prehistoric 46 millennia 46 hominins 46 Kalahari Desert 46 continental crust 46 Homo Sapiens 46 fossils 46 tetrapods 46 savannas 46 continental drift 46 millenniums 46 species extinctions 46 hominid 46 tropical forests 46 mammal species 46 retreating glaciers 46 orchid species 46 Archaeopteryx 46 genetically distinct 45 theropod 45 Precambrian