Related by context. Frequent words. (Click for all words.) 62 meteoroid 61 asteroid 59 asteroids 59 mass extinctions 56 Ocean acidification 55 meteoroids 54 supernova explosion 54 Tunguska 53 species extinctions 53 mass extinction 53 greenhouse warming 53 solar flares 53 super Earths 52 volcanic eruptions 52 supernova explosions 52 retreating glaciers 52 moon Europa 52 explosive eruptions 52 anthropogenic climate 51 volcanism 51 spherules 51 methane hydrates 51 geomagnetic storms 51 comet 51 NEOs 51 galaxy formation 51 rocky planets 51 Cambrian explosion 51 megafauna 51 Earth magnetosphere 51 habitable planets 51 supercontinent 51 habitable planet 50 alien civilizations 50 methane hydrate 50 lithosphere 50 astrobiologists 50 Titan Saturn 50 Younger Dryas 50 Cascadia Subduction Zone 50 magnetosphere 50 planetary 50 Volcanic eruptions 49 terrestrial planets 49 melting permafrost 49 ocean acidity 49 dwarf galaxies 49 stratospheric ozone 49 Gliese #g 49 planetary nebulae 49 atmospheric CO 49 abiotic 49 meteorites 49 Greenland glaciers 49 gamma ray burst 49 interplanetary spacecraft 49 Kuiper belt 49 scarps 49 landmasses 49 terrestrial ecosystems 49 outer planets 49 volcanic activity 49 Galaxy Evolution 48 atmospheric methane 48 comets 48 ejecta 48 GRBs 48 meteor 48 Saturn moons 48 orbital debris 48 Jupiter moons 48 volcanoes 48 solar nebula 48 astrophysical 48 Polar Regions 48 gas hydrates 48 continental crust 48 coronal mass ejections 47 marine sediments 47 geomagnetic storm 47 equatorial regions 47 planetoid 47 solar irradiance 47 climate modelers 47 sunspot cycle 47 Geoengineering 47 Pan STARRS 47 atmospheric carbon dioxide 47 crustal 47 cosmic ray 47 Meridiani 47 geologically active 47 substorms 47 volcano eruptions 47 extinctions 47 Saturn moon 47 planet 47 X ray emission 47 dwarf galaxy 47 Comet Tempel 1 47 biodiversity hotspots