Final answer:
LUCA, the Last Universal Common Ancestor, is a term for the earliest cellular life that led to all modern life on Earth, existing around 3.5 billion years ago. It was a primitive prokaryote with DNA and RNA, and its presence preceded the evolution of complex metabolic processes, including photosynthesis and cellular respiration. The transition from chemical simplicity to biochemical complexity allowed for the divergence into various life forms, including bacteria and archaea.
Step-by-step explanation:
The last Universal Common Ancestor (LUCA) stands for the hypothetical early cell (or group of cells) that gave rise to all subsequent life on Earth. This early form of life is believed to have existed around 3.5 billion years ago and would have been prokaryotic, lacking a nucleus and other membrane-bound organelles. The characteristics of LUCA suggest it had escaped the RNA world, possessing DNA, RNA, and the capability to translate mRNA into polypeptides within a semipermeable phospholipid bilayer. Regarding the divergence of early cellular life into modern cellular life forms such as bacteria and archaea, there was likely a process of metabolisms becoming increasingly regulated and coordinated, which led from chemical simplicity to biochemical complexity. The evolution of cellular respiration occurred after the development of photosynthesis, which allowed for the utilization of oxygen released into the atmosphere. It is suggested that autotrophs, which produce their food using light or chemical energy, may have evolved first. This is because they provided a basic source of energy that could support the later-evolving heterotrophs, which consume other organisms or substances for sustenance.
As cellular life evolved, these metabolic processes were refined and became the basis for further diversification and spread of different life forms. The complexity of life as we know it today is a result of continued evolution, starting from LUCA and culminating in the vast biodiversity present on Earth.