<span>Quoting, Paraphrasing. Things like that.</span>
Answer:
Transformation in thinking that occurred in the 1500's and 1600's caused by scientific observation, experimentation, and questioning of traditional opinions. It changed the way Europeans looked at the world. What did the Greek astronomer Ptolemy believe? He believed the Earth was the center of the universe.
Explanation:
Cyanobacteria, also known as "blue-green algae", are the unicellular organisms which are able to produce oxygen.
Approximately 540 years ago, the atmosphere was very poor on oxygen. Cyanobacteria are thought to be responsible for the oxidization of the atmosphere back then, in an event known as <em>"The Great Oxygenation Event"</em>. As a result, Earth's life forms suffered drastic changes in their composition, as they evolved from being <em>anaerobic</em> to becoming organisms <em>highly dependant</em> on oxygen. The oxygenation of the atmosphere would eventually provide the adequate environment in order for the <em>Cambrian Explosion</em>, or the first diversification of living organisms, to happen.
The Calhoun doctrine shows that Calhoun wanted states to have the right to nullify national laws
