5. As earth cooled, carbon dioxide dissolved in the early ocean. Cyanobacteria consumes carbon dioxide and converted it to oxygen. Methane was removed from the atmosphere as oxygen was produced, eventually leading to the Cambrian explosion.
6. Metabolic processes that use oxygen produce more energy than anaerobic metabolism. Simple diffusion of oxygen would limit the size of a multicellular eukaryote, but animals evolved ways to transport oxygen to their tissues, which permitted an increase to their size.
(6. As earth cooled, carbon dioxide dissolved in the early ocean. Cyanobacteria consumes carbon dioxide and converted it to oxygen. Methane was removed from the atmosphere as oxygen was produced, eventually leading to the Cambrian explosion.
(7. Metabolic processes that use oxygen produce more energy than anaerobic metabolism. Simple diffusion of oxygen would limit the size of a multicellular eukaryote, but animals evolved ways to transport oxygen to their tissues, which permitted an increase to their size.
In Dred Scott v. Sandford (argued 1856 -- decided 1857), the Supreme Court ruled that Americans of African descent, whether free or slave, were not American citizens and could not sue in federal court. The Court also ruled that Congress lacked power to ban slavery in the U.S. territories.
