Although bacterial cell remains are so small that they are difficult to interpret, the Warrawoona fossils are associated with isotopically light carbon, indicative of photosynthetic activity. Abiotic sediments which bear carbon, in contrast, have a relatively greater abundance of heavier carbon isotopes, as compared to carbon within living and fossil algae, plants, and cyanobacteria. From 3.5 billion to 2.0 billion years ago, cyanobacterial photosynthesis provided the ocean with its first abundant dissolved oxygen. This is evidenced by the deposition of banded iron formations , marine sedimentary rocks that include layers rich in iron oxide. Eukaryotes include animals, plants, algae, fungi, and protozoans.
Aerobic organisms use oxygen to obtain energy from their food.
This odd pattern of DNA distribution and similarities to specific bacterial lineages has prompted general acceptance of the Endosymbiont Hypothesis , which states that the eukaryotic cell with its multiple DNA sources arose from symbiosis of a number of prokaryote cells. Chemical fossils indicative of eukaryotic life go back even farther, to 2.7 billion years before present. If you are interested in these ideas, you can click here , and additional material is available in your text. These ideas will not be covered on the exam.