First Prokaryotes: They evolved from replicating molecules and before LUCA (also a prokaryote). Prokaryotes lack a nucleus and organelles. Although research continues identifying when the first true prokaryotes evolved, it is believed they evolved sometime between 3.8 to 4 billion years ago. While the earliest prokaryotes are part of our direct-line ancestors, today we know their descendants as bacteria and archaea. Bacteria is part of our common knowledge, but archaea are mostly known to microbiologists because they mainly live in extreme temperatures. Interestingly, viruses are neither these prokaryotes nor later eukaryotes. They are a holdover from before prokaryotes and are not considered life.

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