ONCE upon a time, 3 ga BP, there lived a single organism called LUCA. It was enormous, a mega-organism like none seen since, it filled the planet's oceans before splitting into 3 and giving birth to the ancestors of all living things on Earth today.
by comparing their sequence of DNA letters, genes can be arranged in evolutionary family trees, a property that enabled Dr. Martin and his colleagues to assign the 6m genes to a much smaller number of gene families. Of these, only 355 met their criteria for having probably originated in Luca, the joint ancestor of bacteria and archaea. The 355 genes pointed quite precisely to an organism that lived in the conditions found in deep sea vents, the gassy, metal-laden, intensely hot plumes caused by seawater interacting with magma erupting through the ocean floor. Dr. Sutherland too gave little credence to the argument that Luca might lie in some gray transition zone between nonlife and life just because it depended on its environment for some essential components. “It’s like saying I’m 50% alive because I depend on my local supermarket.”
2024-07-10: Primordial LUCA Dating
Molecular clock analysis and genomic reconstruction date the Last Universal Common Ancestor (LUCA) to 4.2 billion years ago—only 300 million years after Earth's formation. LUCA already possessed a 2.5-megabase genome with an active primordial immune system and sulfur-metabolizing enzymes, proving that the transition from prebiotic chemistry to functional cellular genetics occurred remarkably rapidly. science.org