Related by context. Frequent words. (Click for all words.) 56 nitrogen fixation 55 multicellular organisms 53 asexual reproduction 53 resorption 52 embryogenesis 52 microfossils 52 desiccation 52 solar nebula 52 oxidization 52 abiotic 52 marine sediments 52 speciation 52 Cambrian explosion 51 diatom 51 morphologies 51 radioactive decay 51 melanosomes 51 tetrapod 51 mummification 50 evolutionary adaptation 50 prokaryotes 50 radiocarbon dating 50 isotopic composition 50 Poinar 50 glaciation 50 malignant transformation 50 calcite 49 soft tissues 49 spermatogenesis 49 fossils 49 zircons 49 stromatolites 49 terrestrial ecosystems 49 prions 49 hominins 49 mammalian brain 49 Ardipithecus 49 collagen fibers 49 nonliving 48 nacre 48 radiocarbon 48 photosynthesis 48 Oxidative stress 48 multicellular 48 fossilized 48 evolutionary 48 decomposition 48 ossification 48 parthenogenesis 48 Late Cretaceous 48 plate tectonics 48 decay 48 neural tissue 48 genetic alteration 48 eukaryotic cells 48 ribozyme 48 landforms 47 bipedalism 47 mammalian species 47 stem cell differentiation 47 Tiktaalik 47 diatoms 47 oxidation 47 prion protein 47 lake sediments 47 Precambrian 47 prion disease 47 pathophysiological 47 myelination 47 megafauna 47 eukaryotes 47 extirpation 47 poorly understood 47 Burgess Shale 47 irreducible complexity 47 hadrosaur 47 macroscopic 47 misfolding 47 Carboniferous 46 labile 46 nucleation 46 prehistory 46 isotopic 46 naturally occurring 46 coprolites 46 biological molecules 46 paleoanthropologist 46 tetrapods 46 biochemical reactions 46 chemical reactions 46 plasticity 46 Radiocarbon dating 46 putrefaction 46 morphological 46 organism 46 fossil 46 microbiome 46 vertebrate 46 organisms 46 morphologically 46 Cyanobacteria