Emergence of eukaryotes
Further information: Eukaryote § Origin of eukaryotes Chloroplasts in the cells of a moss Modern taxonomy classifies life into three domains. The time of their origin is uncertain. The Bacteria domain probably first split off from the other forms of life (sometimes called Neomura ), but this supposition is controversial. Soon after this, by 2 Ga,the Neomura split into the Archaea and the Eukarya . Eukaryotic cells (Eukarya) are larger and more complex than prokaryotic cells (Bacteria and Archaea), and the origin of that complexity is only now becoming known. [ citation needed ] Around this time, the first proto-mitochondrion was formed. A bacterial cell related to today's Rickettsia ,which had evolved to metabolize oxygen , entered a larger prokaryotic cell, which lacked that capability. Perhaps the large cell attempted to digest the smaller one but failed (possibly due to the evolution of prey defen...