ABSTRACT
Life evolved almost 4 billion years ago with the formation of the rst cell, which is known as the rst universal common ancestor (FUCA) of all subsequent cells, which probably had an RNA-based genome. is very primitive cell evolved, increasing its abilities and acquiring a DNA-based genome, and so became the last universal common ancestor (LUCA), whose progeny diverged to become the future eubacteria and the archaebacteria. A little later, cyanobacteria evolved; their ability to photosynthesize and so produce oxygen led to the Great Oxygenation Event ~2.45 Bya and a change in the earth’s atmosphere. Around 2 Bya, eukaryotes started to evolve. It is now clear that the rst eukaryotic common ancestor (FECA) acquired the genes for its nucleus mainly through endosymbiosis of an archaebacterium and, much later, its mitochondria from endosymbiosis of a further eubacterium. Once organelles had been acquired, this cell evolved to become the last eukaryotic common ancestor (LUCA) of all future eukaryotes. e plant and algal clades diverged from the others through endosymbiosis of a cyanobacterium to give a chloroplast and the acquisition of two agella, while the fungal and animal worlds had a single agellum. Plant, algal, and fungal cells also became distinguished from animal cells through acquiring various polysaccharide cells walls, with all being in place soon after 900 Mya. is chapter looks at the phylogenetic, timing, and other evidence on which this early history of life is built.
