What drove circadian rhythms to evolve has been an enigmatic question. Previous hypotheses emphasized that photosensitive proteins and circadian rhythms may have originated together in the earliest cells, with the purpose of protecting replicating DNA from high levels of damaging ultraviolet radiation during the daytime. As a result, replication was relegated to the dark. However, evidence for this is lacking, since the simplest organisms with a circadian rhythm, the cyanobacteria, do the opposite of this - they divide more in the daytime. Recent studies instead highlight the importance of co-evolution of redox proteins with circadian oscillators in all three kingdoms of life following the Great Oxidation Event approximately 2.3 billion years ago. The current view is that circadian changes in environmental oxygen levels and the production of reactive oxygen species (ROS) in the presence of daylight are likely to have driven a need to evolve circadian rhythms to preempt, and therefore counteract, damaging redox reactions on a daily basis.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): What environmental event occurred 2.3 million years ago?
Ah, so.. Great Oxidation Event

On 26 June 1950, the National Assembly supported a crucial bill written by Milovan Đilas and Tito about "self-management" (samoupravljanje): a type of cooperative independent socialist experiment that introduced profit sharing and workplace democracy in previously state-run enterprises which then became the direct social ownership of the employees. On 13 January 1953, they established that the law on self-management was the basis of the entire social order in Yugoslavia. Tito also succeeded Ivan Ribar as the President of Yugoslavia on 14 January 1953. After Stalin's death Tito rejected the USSR's invitation for a visit to discuss normalization of relations between two nations. Nikita Khrushchev and Nikolai Bulganin visited Tito in Belgrade in 1955 and apologized for wrongdoings by Stalin's administration. Tito visited the USSR in 1956, which signaled to the world that animosity between Yugoslavia and USSR was easing. However, the relationship between the USSR and Yugoslavia would reach another low in the late 1960s. Commenting on the crisis, Tito concluded that:
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): When did Tito visit the USSR to signal that his country's animosity was decreasing?
Ah, so.. 1956

The largest and bloodiest American battle came at Okinawa, as the U.S. sought airbases for 3,000 B-29 bombers and 240 squadrons of B-17 bombers for the intense bombardment of Japan's home islands in preparation for a full-scale invasion in late 1945. The Japanese, with 115,000 troops augmented by thousands of civilians on the heavily populated island, did not resist on the beaches—their strategy was to maximize the number of soldier and Marine casualties, and naval losses from Kamikaze attacks. After an intense bombardment the Americans landed on 1 April 1945 and declared victory on 21 June. The supporting naval forces were the targets for 4,000 sorties, many by Kamikaze suicide planes. U.S. losses totaled 38 ships of all types sunk and 368 damaged with 4,900 sailors killed. The Americans suffered 75,000 casualties on the ground; 94% of the Japanese soldiers died along with many civilians.
If it is possible to answer this question, answer it for me (else, reply "unanswerable"): How many U.S. ships were lost at Okinawa?
Ah, so..
38