Related by context. Frequent words. (Click for all words.) 52 Industrial Revolution 48 Neolithic 47 Paleolithic 47 Pliocene 46 gigatonnes 45 #th century 45 drylands 45 Little Ice Age 45 hunter gatherers 44 Fertile Crescent 44 atmospheric concentrations 44 Bronze Age 44 medieval 44 prehistory 44 CO2 concentrations 44 atmospheric CO2 44 millennia 44 antiquity 43 prehistoric 43 Medieval Warm Period 43 millenniums 43 Middle Ages 43 agrarian society 43 midcentury 43 aridity 42 Late Cretaceous 42 ancient civilizations 42 atmospheric carbon dioxide 42 croplands 42 subsistence 42 Sumerians 42 Hellenistic 42 urbanization 42 epochs 42 civilization 42 greenhouse gas concentrations 42 landmass 42 twentieth century 42 radiocarbon 42 centuries 41 Roman empire 41 millennium BC 41 sea 41 fifteenth century 41 Han Dynasty 41 glaciation 41 inhabitants 41 Roman Empire 41 ancient civilization 40 Mayan civilization 40 glacial ice 40 Homo sapiens 40 hunter gatherer 40 oceans 40 #BC [003] 40 Mesoamerica 40 subsistence farming 40 decadal 40 arable land 40 industrialized 40 subsistence agriculture 40 gigatons 40 suburbanization 40 Persian Empire 39 ancient 39 ancestors 39 pre Columbian 39 pharaohs 39 latitudes 39 civilizations 39 troposphere 39 urbanized 39 deforested 39 glacial melt 39 earths 39 coarse grains 39 modern 39 Tibetan Plateau 39 megafauna 39 vertebrates 39 nineteenth century 39 Arctic tundra 39 Ottoman empire 39 biosphere 39 inhabited 38 undernourishment 38 pharaonic 38 Coral reefs 38 primitive 38 Neandertals 38 temperate regions 38 Per capita income 38 hominids 38 Pleistocene 38 Westernization 38 Ming dynasty 38 Pharaonic 38 radiocarbon dating 38 seafaring 38 ecologies 38 extinctions