Related by context. Frequent words. (Click for all words.) 63 mass extinctions 60 Cambrian explosion 59 supernova explosion 59 supercontinent 57 supernova explosions 56 Younger Dryas 56 solar nebula 56 atmospheric methane 55 mass extinction 54 magnetar 54 Antarctic ozone 54 prokaryotes 54 gamma ray burst 53 single celled 53 megafauna 53 planetary nebula 53 supernova remnants 53 Cretaceous Period 52 interglacial period 52 volcanism 52 diatoms 52 supernovae 52 substorms 52 Gamma ray bursts 52 meteoroid 52 globular clusters 52 X ray emission 52 scientists theorize 52 Galaxy Evolution 52 atmospheric carbon dioxide 51 supernova 51 supernova remnant 51 supernovas 51 Eta Carinae 51 dwarf galaxy 51 single celled organisms 51 Phaethon 51 gamma ray bursts 51 Ocean acidification 51 Little Ice Age 50 Crab Nebula 50 subatomic particle 50 sunspot activity 50 quark gluon plasma 50 upwelling 50 biogenic 50 planetary nebulae 49 quasar 49 dinosaurs 49 species extinctions 49 radioactive decay 49 Late Cretaceous 49 GRBs 49 quasars 49 trilobites 49 extinctions 49 stromatolites 49 radiative forcing 49 diatom 49 galaxy formation 49 accretion disk 49 distant galaxy 49 Saturn moons 48 Halley comet 48 vertebrate species 48 mammals 48 marine sediments 48 evolutionary adaptation 48 Carboniferous 48 Titan Saturn 48 Saturn rings 48 marine invertebrates 48 abundances 48 auroral 48 Ordovician 48 terrestrial planets 48 multicellular 48 ejecta 48 neutron star 48 aerosol particles 48 archaea 48 Bose Einstein condensate 48 comets 48 explosive eruptions 48 tyrannosaur 48 fossil 48 neutron stars 47 microfossils 47 plate tectonics 47 atmospheric circulation 47 habitable planets 47 atmospheric CO 47 ocean acidity 47 marine reptiles 47 rocky planets 47 comet 47 glaciation 47 coronal mass ejections 47 phytoplankton 47 Astrophysicists 47 plankton