Related by context. Frequent words. (Click for all words.) 64 mass extinctions 60 mass extinction 56 dinosaurs 56 supernova explosion 55 megafauna 55 extinctions 53 plate tectonics 52 single celled organisms 52 greenhouse warming 52 volcanism 51 GRBs 51 Archaeopteryx 51 glaciation 51 fossil 51 extrasolar planets 51 comets 51 elliptical galaxies 50 supernova explosions 50 fossils 50 volcanic eruptions 50 mammoths 50 Saturn rings 50 mammals 50 asteroid 50 tetrapods 50 Homo sapiens 49 Eta Carinae 49 woolly mammoths 49 fossilized remains 49 evolutionary biologists 49 meteorite 49 sunspot activity 49 gamma ray burst 49 exoplanets 49 single celled 49 globular clusters 48 atmospheric carbon dioxide 48 sauropods 48 comet 48 rocky planets 48 pulsar 48 meteorites 48 cosmic rays 48 Neandertals 48 gamma ray bursts 48 planets 48 Homo floresiensis 48 quasars 47 cosmologists 47 supernovas 47 supernova 47 tyrannosaurs 47 asteroids 47 diatoms 47 journal Geology 47 T. rex 47 Late Cretaceous 47 Iapetus 47 arthropods 47 sunspots 47 Little Ice Age 47 neutron stars 47 hominid 47 Precambrian 47 vertebrates 47 pterosaurs 47 palaeontologists 46 galaxy clusters 46 atmospheric circulation 46 species extinctions 46 ejecta 46 meteor 46 astrophysicists 46 supernovae 46 paleontologists 46 speciation 46 bee populations 46 sauropod 46 hominids 46 astronomers 46 phylogeny 46 Tunguska 46 lichens 46 comet dust 46 flowering plants 46 dwarf galaxy 46 PETM 46 Mayan calendar 46 gravitational waves 45 X ray emission 45 neutron star 45 eukaryotes 45 vortices 45 cometary 45 evolutionists 45 melting permafrost 45 vertebrate 45 super Earths 45 subatomic particles 45 theropods 45 nebula