Related by context. Frequent words. (Click for all words.) 66 mass extinctions 63 mass extinction 61 glaciation 58 speciation 58 Late Cretaceous 57 extinctions 56 supernova explosion 56 Pleistocene 55 Precambrian 55 single celled organisms 55 diatoms 54 megafauna 54 eukaryotes 54 Ordovician 54 single celled 53 dinosaurs 53 vertebrate 53 volcanism 53 vertebrates 53 evolutionary 53 Mesozoic 53 tetrapods 52 Cretaceous 51 Homo sapiens 51 PETM 51 mammals 51 Little Ice Age 51 Triassic 51 Pliocene 51 Australopithecus 50 hominid 50 hominids 50 flowering plants 50 fossils 50 plate tectonics 49 common ancestor 49 lineages 49 epochs 49 supernova 49 supernova explosions 49 supernovae 49 Archaeopteryx 49 taxa 49 Eocene 48 Holocene 48 atmospheric carbon dioxide 48 Homo erectus 48 evolution 47 fossil 47 domestication 47 cyanobacteria 47 prehistory 47 phylogeny 47 gamma ray burst 47 sunspot 47 theropods 46 GRBs 46 mammalian 46 mammoths 46 Fertile Crescent 46 Big Bang 46 fossilized remains 45 amphibian species 45 morphological 45 supernovas 45 archaea 45 anoxic 45 sauropods 45 C. elegans 45 quasars 45 scientists theorize 44 globular clusters 44 sunspots 44 gamma ray bursts 44 pterosaurs 44 Industrial Revolution 44 Ice Age 44 humans 44 evolutionary biologists 44 mammal species 44 Medieval Warm Period 44 Paabo 44 Eta Carinae 44 alternative splicing 44 lifeforms 44 El Ninos 44 sea anemones 44 Neandertals 44 sauropod 44 abundances 44 species 44 biosphere 44 coalescence 44 greenhouse warming 44 tyrannosaurs 44 comets 44 hydrothermal vents 44 influenza pandemics 44 galaxies 44 organic molecules 44 cosmic microwave background