Related by context. Frequent words. (Click for all words.) 61 supernova explosion 58 mass extinction 58 Chicxulub 57 mass extinctions 57 Cambrian explosion 57 Snowball Earth 56 Younger Dryas 56 glaciations 55 atmospheric methane 53 interglacial period 52 Antarctic ozone 52 meteoroid 52 supercontinent 52 WASP #b 52 Jurassic Period 51 Anthropocene 51 Galileo spacecraft 51 Cretaceous Period 51 Gliese #g 50 solar nebula 50 Ardipithecus ramidus 50 dwarf galaxy 50 Cosmologists 50 asteroid 50 planetesimals 50 Tunguska 50 megafauna 50 subatomic particle 50 glaciation 49 interglacial 49 Higgs particle 49 Oort Cloud 49 extinctions 48 paleoclimate 48 magnetic reconnection 48 multicellular 48 greenhouse warming 48 microfossils 48 gamma ray burst 48 volcanism 48 supernova explosions 48 Little Ice Age 48 microlensing 48 planetary nebula 48 fossilization 48 Eta Carinae 48 plate tectonics 48 magnetars 48 hydrothermal activity 47 geomagnetic storm 47 Phaethon 47 Jupiter moons 47 galaxy formation 47 GRB # 47 dinosaurs 47 radioactive decay 47 prokaryotes 47 Martian rocks 47 observable universe 47 magnetar 47 comet nucleus 47 marine sediments 46 Hubble observations 46 ejecta 46 isotopic 46 vertebrate species 46 dinosaurs roamed 46 Climategate scandal 46 retreating glaciers 46 isotopic composition 46 cometary 46 innermost planet 46 elemental composition 46 moonlets 46 Radiocarbon dating 46 Brownian motion 46 Galaxy Evolution 46 planetoid 46 impactor 46 faunal 46 Homo sapiens 46 tyrannosaur 45 planet orbiting 45 Carboniferous 45 planetary 45 spherules 45 substorms 45 explosive eruptions 45 Mars Pathfinder 45 sunspot cycle 45 phylogeny 45 Itokawa 45 Archaeopteryx 45 NASA Stardust spacecraft 45 cosmic microwave background 45 Indohyus 45 perihelion 45 comet Wild 45 Lake Vostok 45 H. erectus 44 species extinctions