The Last Universal Common Ancestor (LUCA) is the hypothetical single-celled organism from which all life on Earth (Bacteria, Archaea, Eukarya) descended, existing billions of years ago, possibly around 4.2 billion years ago in hydrothermal vents, possessing key genetic machinery like DNA/RNA and ribosomes, and representing the root of the universal tree of life. Researchers reconstruct LUCA by finding genes and traits common to all present-day life, revealing a complex microbe that harnessed natural chemical energy, likely used hydrogen and carbon dioxide, and had basic defense systems, forming the foundation for all subsequent evolution.
