Related by context. Frequent words. (Click for all words.) 63 landmasses 60 Gondwana 58 glaciation 57 Late Cretaceous 56 sedimentary rock 56 plate tectonics 56 tetrapods 56 megafauna 56 Saturn rings 56 volcanism 55 single celled organisms 55 Ordovician 54 supernova explosion 54 Earth crust 54 Homo sapiens 54 Pleistocene 53 Precambrian 53 Mesozoic 53 common ancestor 53 Iapetus 53 Neandertals 53 mass extinction 53 Milky Way Galaxy 52 Cretaceous 52 single celled 52 dinosaurs 52 terrestrial planets 52 Little Ice Age 52 earth crust 52 galaxy clusters 52 hominids 52 volcanic islands 51 crustal 51 landmass 51 Triassic 51 mass extinctions 51 Ellesmere Island 51 globular clusters 51 tyrannosaurs 51 calcite 51 rocky planets 51 theropods 51 Kuiper Belt 50 Homo erectus 50 Neanderthals 50 archaea 50 galaxies 50 diatoms 50 organic molecules 50 comets 50 Fertile Crescent 50 ejecta 50 epochs 49 Pliocene 49 galaxy cluster 49 olivine 49 subduction zone 49 spacetime 49 subduction zones 49 Australopithecus 49 Saturn moons 49 quasars 49 neutron star 49 spiral galaxies 49 Itokawa 49 supernova explosions 49 Eocene 49 magnetosphere 49 fossils 49 Paleozoic 49 cosmic microwave background 49 planets 49 eukaryotes 49 quasar 48 Medieval Warm Period 48 Paabo 48 Milky Way galaxy 48 sedimentary rocks 48 Proterozoic 48 hominid 48 silicates 48 supernovae 48 lava flows 48 neutron stars 48 gamma ray burst 48 supernovas 48 Sedna 48 glacial ice 48 mammoths 48 interstellar medium 48 seamounts 48 subduction 48 lineages 48 caldera 48 hydrothermal vents 48 sauropods 47 asteroid belt 47 nebula 47 atomic particles 47 atomic nuclei 47 equatorial regions