Related by context. Frequent words. (Click for all words.) 46 rocky planets 46 single celled 45 single celled organisms 45 theorize 45 atomic particles 44 microscopic organisms 43 cosmologists 43 radioactive decay 43 diatoms 43 comets 43 galaxy clusters 43 meteorites 43 humans 42 supernova explosions 42 biochemical reactions 42 subatomic particles 42 archaea 42 super Earths 42 cosmic microwave background 42 volcanism 42 biochemical processes 42 chemical reactions 41 terrestrial planets 41 gamma ray bursts 41 organic molecules 41 interstellar medium 41 GRBs 41 Little Ice Age 41 nerve cells 41 subduction zones 41 Higgs boson 40 trillionth 40 upwelling 40 nuclei 40 ejecta 40 comet nucleus 40 silicates 40 atomic nucleus 40 neutron stars 40 poorly understood 39 hydrogen atoms 39 organic compounds 39 supernova explosion 39 volcanic eruptions 39 particles 39 magnetosphere 39 polar caps 39 oxidants 39 protons 39 primordial soup 39 supernovae 39 Big Bang theory 39 quasar 38 epochs 38 Saturn moons 38 galaxies 38 elliptical galaxies 38 Earth crust 38 mass extinction 38 coronal mass ejections 38 Big Bang 38 supernovas 38 celestial bodies 38 winter solstice 38 water vapor 38 comet 38 Meteorites 38 atoms 38 gluons 37 globular clusters 37 neutron star 37 extrasolar planet 37 gravitational waves 37 spacetime 37 calcite 37 supernova 37 glaciation 37 dwarf galaxy 37 theorized 37 hypothesised 37 megafauna 37 solar flares 36 distant galaxy 36 quasars 36 planets 36 Perseids 36 atomic nuclei 36 iron oxides 36 outer layers 36 supermassive black holes 36 simplest explanation 36 heliosphere 36 interstellar space 36 vernal equinox 36 gamma rays 36 spring equinox 36 Saturn rings 36 exoplanets 36 subatomic 36 neutrons 36 equatorial regions