Related by context. Frequent words. (Click for all words.) 62 microfossils 61 stromatolites 57 lava tubes 57 foraminifera 57 coprolites 55 marine sediments 55 snail shells 54 isotope ratios 54 radiocarbon dated 53 salt crystals 53 fossils 53 spectral signatures 53 igneous rocks 53 aragonite 53 chemical composition 53 elemental composition 53 oxygen isotopes 53 ammonites 53 landforms 53 middens 52 fossil specimens 52 volcanic vents 52 preserved fossils 52 trilobites 52 Martian rocks 52 Palaeolithic 51 prehistoric 51 trackways 51 isotopic composition 51 sediment cores 51 Cyanobacteria 51 Radiocarbon dating 51 amphorae 51 lunar soil 51 microenvironments 51 vertebrate animals 51 trackway 51 igneous rock 50 Soil samples 50 astrobiologists 50 naturally occurring mineral 50 mud volcanoes 50 lake sediments 50 stalagmite 50 rock outcrops 50 noble gases 50 nonliving 50 stalagmites 50 spherules 50 zeolites 50 Martian landscape 50 nanobubbles 50 geomorphology 49 flint tools 49 radiocarbon dating 49 termite mounds 49 nanosized 49 morphologies 49 slime molds 49 Lake Vostok 49 calcareous 49 ALH# 49 baleen whale 49 physicochemical 49 Fossilized 49 Earthlike 49 dinosaur fossils 49 zircons 49 hydrothermal vent 49 radiocarbon 49 hieroglyphs 49 lichens 48 undersea volcanoes 48 faunal 48 Viking landers 48 metamorphic rocks 48 feathered dinosaurs 48 pictographs 48 nanoclusters 48 arthropod 48 lava tube 48 striations 48 Palaeontologists 48 cenotes 48 underwater volcanoes 48 mussel shells 48 microorganisms 48 red ocher 48 fossilized bones 48 stalactite 48 biogenic 48 sedimentary rock 48 limestone caves 47 mosaic floors 47 fragments 47 engineered nanoparticles 47 meteorites 47 hadrosaur 47 iron oxides 47 fossilized remains 47 dinosaur footprints