What is Life?

Source Institution: Smithsonian National Museum of Natural History

Source Exhibit: David H. Koch Hall of Fossils - Deep Time

Source Url: https://naturalhistory.si.edu/visit/virtual-tour/current-exhibits/deep-time-virtual-tour-fossil-list

Source Kind: interpretive_topic_or_panel

Use: research inspiration only; SAGE will write original interpretation

Dossier Status: scientifically_enriched_concept_room_01

Plain Language Explanation: Life is easy to recognize in familiar organisms but surprisingly difficult to define with one perfect rule. Living systems on Earth use chemistry to maintain organized processes, obtain and transform energy, store and transmit information, reproduce at the population level and evolve. A widely used astrobiology working definition describes life as a self-sustaining chemical system capable of Darwinian evolution, but scientists do not treat that wording as the final answer to every edge case.

Evidence: All known cellular life carries hereditary information and maintains organized biochemical processes.; Populations of living organisms undergo heritable change through evolution.; Viruses and laboratory chemical systems demonstrate why the boundary between life and non-life can be difficult to define with one simple checklist.

Examples From Collection: Grypania sp.; Conophyton sp.; Stromatolites show that ancient life may be recognized through structures produced by microbial communities rather than through preserved individual cells.

Common Misconception: Movement does not define life. Plants, fungi and many microorganisms may not move from place to place, while nonliving processes such as fire can spread and consume energy.

What Scientists Still Debate: There is no universally accepted definition that cleanly handles every case, especially viruses, artificial chemical systems and hypothetical life unlike Earth's organisms.

Sources: https://science.nasa.gov/universe/search-for-life/life-on-other-planets-what-is-life-and-what-does-it-need/; https://astrobiology.nasa.gov/education/alp/alive-or-not/

Enrichment Method: SAGE original interpretive concept; source title retained; evidence separated from reconstruction and open questions