Related by context. Frequent words. (Click for all words.) 71 Cretaceous Period 63 Precambrian 62 interglacial 62 multicellular 60 Pleistocene 60 trilobites 59 Late Cretaceous 59 Carboniferous 59 dinosaurs roamed 58 Pliocene 58 Cretaceous 57 mass extinction 57 dinosaurs 56 mass extinctions 56 Ordovician 56 fossils 55 marine sediments 55 multicellular organisms 55 Eocene 55 Mesozoic 55 Triassic 55 glaciation 55 Quaternary 54 fossil 54 anatomically modern 53 Tiktaalik 53 Holocene 53 single celled organisms 52 single celled 52 Ardipithecus 52 lavas 52 Australopithecus 51 fossilized 51 diatoms 51 prehistoric 51 tetrapods 51 megafauna 51 supernova explosion 51 Archaeopteryx 51 sedimentary rock 51 Jurassic 50 tyrannosaur 50 radiocarbon 50 Homo sapiens 50 Homo habilis 50 atmospheric CO 50 Paleolithic 50 Ice Age 50 plate tectonics 50 volcanism 50 PETM 50 Poinar 50 hominid 49 primordial soup 49 Neandertals 49 marine reptiles 49 fossilized remains 49 vertebrates 49 tyrannosaurs 49 theropod 49 plesiosaur 49 genus Homo 49 Lower Cretaceous 49 marine invertebrates 49 continental crust 49 terrestrial ecosystems 48 Paleozoic 48 oxygen isotopes 48 mammoths 48 vertebrate 48 extinctions 48 hadrosaur 48 hominin 48 prehistory 48 Medieval Warm Period 48 archaea 48 sauropod 48 geologic 48 eukaryotes 48 vertebrate species 47 diatom 47 atmospheric CO2 47 radioactive decay 47 atmospheric carbon dioxide 47 Oligocene 47 Little Ice Age 47 Australopithecus afarensis 47 radiocarbon dating 47 Homo erectus 47 morphologies 47 oceanic crust 47 mammals 47 taxa 47 epochs 47 sauropods 46 homo sapiens 46 abundances 46 hominins 46 Devonian 46 hominids 46 Fertile Crescent