| Term | Definition |
|---|
| Colony | A collection of autonomously replicating cells of the same species. |
| Genetic annealing | The production of a new genome through the transfer of part of the genome of one organism to another organism. |
| Geologic record | The division of Earth’s history into time periods, grouped into three eras: Archaean, Proterozoic, Phanerozoic, and further subdivided into eras and epochs. |
| Half-life | The number of years it takes for 50% of a sample of an isotope to decay. |
| Heterocyst | A specialized cell that engages in nitrogen fixation in some filamentous cyanobacteria (formerly called heterocyst). |
| Magnetic reversal | A reversal of the polarity of Earth’s magnetic field. |
| Pangaea | The supercontinent formed near the end of the Paleozoic era when plate movements brought all the landmasses of Earth together. |
| Protobiont | An aggregate of abiotically produced molecules surrounded by a membrane or membrane-like structure. |
| Radiometric dating | A method paleontologists use for determining the ages of rocks and fossils on a scale of absolute time, based on the half-life of radioactive isotopes. |
| Ribozyme | An enzyme-like RNA molecule that catalyzes reactions during RNA splicing. |
| Serial endosymbiosis | A model of the origin of eukaryotes consisting of a sequence of endosymbiotic events in which mitochondria, chloroplasts, and perhaps other cellular structures were derived from small prokaryotes that had been engulfed by larger cells. |
| Snowball Earth | The hypothesis that glaciers covered the planet’s landmasses from pole to pole 750–570 million years ago. |
| Stromatolite | Rocklike structure composed of layers of prokaryotes and sediment. |
| Three-domain system | A system of taxonomic classification based on three “superkingdoms”: Bacteria, Archaea, and Eukarya. |
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