| The evolution of genomic complexity and metabolic pathways during Earth's history. The earliest origin of life is not known. However, assuming a single last universal common ancestor evolved in mid-Proterozoic, there is evidence of microbial life. When oxygenic photosynthesis evolved is not clear, but geochemical data suggest that between about 2.3 and 2.2.billion years ago, there was sufficient oxygen in the atmosphere to permit an ozone layer to form. That singular event appears to have precipitated a massive increase in genome and metabolic complexity, culminating in the rise of metazoans around 600 million years ago, and the rise of terrestrial plants around 430 million years ago. The feedbacks in the evolutionary trajectory have led to increasing genomic and metabolic complexity. (Image and caption courtesy of Science.) |
