Related by context. Frequent words. (Click for all words.) 58 supernova explosion 57 mass extinctions 56 glaciation 55 supernova explosions 54 volcanism 54 hydrological cycle 54 meteoroid 53 olivine 53 sunspot cycle 52 lithosphere 51 X ray emission 51 Gliese #g 51 Earth 51 ejecta 51 scarps 51 cosmic microwave background 51 atmospheric carbon dioxide 51 Saturn rings 50 mass extinction 50 volcanic activity 50 meteoroids 50 cometary 50 glacial melt 50 Cretaceous Period 50 plate tectonics 50 cosmic ray 49 comets 49 gamma ray burst 49 sedimentary rock 49 Little Ice Age 49 radioactive decay 49 Itokawa 49 dwarf galaxies 49 martian 49 meteorites 49 polar caps 49 terrestrial ecosystems 49 sunspot activity 49 dwarf galaxy 48 mid latitudes 48 volcanic eruptions 48 Martian surface 48 globular clusters 48 greenhouse warming 48 comet 48 substorms 48 lake sediments 48 albedo 48 orbiting spacecraft 48 interstellar dust 48 Kuiper belt 47 interglacial 47 greenhouse gas concentrations 47 rocky planets 47 marine sediments 47 earths 47 WMAP 47 quasars 47 regolith 47 GRBs 47 supernovae 47 super Earths 47 lava flows 47 comet nucleus 47 aerosol particles 47 elliptical galaxies 47 magnetar 47 Eta Carinae 47 Opportunity rover 47 oxygen isotopes 47 CO2 concentrations 46 cosmic rays 46 asteroids 46 megafauna 46 supernova 46 isotopic 46 planets 46 Precambrian 46 diatoms 46 calcite 46 comet dust 46 landmasses 46 Martian 46 asteroid 46 sols 46 Jupiter moons 46 crustal 46 Global Surveyor 46 Tibetan Plateau 45 meteorite 45 gigatonnes 45 species extinctions 45 Saturn moon 45 Iapetus 45 atmospheric CO2 45 multicellular organisms 45 deuterium 45 earth crust 45 moons 45 terrestrial planets 45 abundances