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plural LUCAs
(taxonomy, biology, paleontology) Initialism of last universal common ancestor; the hypothesised most recent primordial organism that is an ancestor to all organisms now living. quotations
Luca is now usually placed deep underground, in a fissure in hot igneous rocks, where she fed on sulphur, iron, hydrogen and carbon.
1999, Matt Ridley, Genome, Harper Perennial, published 2000, page 19
It was around 2.9 billion years ago that LUCA split into the three domains of life: the single-celled bacteria and archaea, and the more complex eukaryotes that gave rise to animals and plants […] .
2011 November 26, Michael Marshall, “Our ancestor, the mega-organism”, in New Scientist, page 8