The oldest fossil record of life on earth is photosynthesizing cyanobacteria found in stromatolites. However, photosynthesis is a complex process, and these cyanobacteria probably had precursors that are yet unknown. What were these first hypothetical life forms like?
To answer that question we must first decide on a definition of what constitutes a living thing. This definition is not as clear-cut as it might appear.
Living things grow and reproduce, but inorganic crystals do this, too. Viruses are not regarded as living, as they require a host in order to survive and reproduce, but the existence of viruses highlights the fuzzy line between life and non-life, and reflects the fact that life must have originated from a non-living, “prebiotic” stage.
The British biologist J.B.S. Haldane concluded that “The line between living and dead matter is …somewhere between a cell and an atom.”
Photo and information on research on artificial life here.
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