Related by context. Frequent words. (Click for all words.) 69 glaciation 63 mass extinctions 63 mass extinction 62 volcanism 59 greenhouse warming 59 megafauna 59 Little Ice Age 58 Pleistocene 58 plate tectonics 58 Medieval Warm Period 56 Pliocene 55 Precambrian 54 Antarctic Ice 53 Holocene 53 polar caps 53 supernova explosion 53 Oetzi 52 ENSO 52 Ordovician 52 diatoms 52 atmospheric circulation 52 mammoths 52 atmospheric CO2 51 permafrost 51 Martian 51 sunspot activity 51 PETM 51 Tibetan Plateau 51 mid latitudes 51 Nature Geoscience 51 atmospheric carbon dioxide 51 upwelling 51 Greenland ice 51 Cretaceous 51 volcanic eruptions 50 moon Europa 50 polar regions 50 glaciers 50 CO2 concentrations 50 Mesozoic 50 martian 49 Antarctic ice 49 Eocene 49 landforms 49 lake sediments 49 radiocarbon 49 Astrobiology 49 woolly mammoths 49 Martian surface 48 geologic 48 Saturn moon 48 radioactive decay 48 dinosaurs 48 hydrothermal vents 48 polar 48 supernova explosions 48 magmatic 48 Tunguska 48 geologically active 48 desiccation 48 Ice Age 48 glacial ice 47 mountain glaciers 47 sedimentary rock 47 ejecta 47 polar ice 47 olivine 47 anthropogenic 47 Enceladus 47 scientists theorize 47 IPY 47 prehistory 47 volcanic activity 47 glacial 47 albedo 47 journal Geophysical Research 47 paleo 47 comets 47 acidification 47 astrophysical 47 Antarctica 47 organic molecules 47 melting permafrost 47 cosmologists 47 oxygen depletion 47 sediments 46 atmospheric concentrations 46 prehistoric 46 NSIDC 46 cyanobacteria 46 El Niño 46 sediment cores 46 fossils 46 gas hydrates 46 radiocarbon dating 46 rocky planets 46 biosphere 46 extinctions 46 climatic 46 cosmic microwave background 46 hydrothermal