On Thursday, September 19, 1985, at 7:19 am local time, Mexico City was struck by an earthquake of magnitude 8.1 on the Richter scale. Although this earthquake was not as deadly or destructive as many similar events in Asia and other parts of Latin America, it proved to be a disaster politically for the one-party government. The government was paralyzed by its own bureaucracy and corruption, forcing ordinary citizens to create and direct their own rescue efforts and to reconstruct much of the housing that was lost as well.
How strong was the powerful earthquake that hit Mexico City in 1985?
8.1 on the Richter scale

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.
What is thought that circadian rhythm evolved to protect?
replicating DNA

In addition to his many other roles, the emperor acted as the highest priest in the land who made sacrifices to Heaven, the main deities known as the Five Powers, and the spirits (shen ) of mountains and rivers. It was believed that the three realms of Heaven, Earth, and Mankind were linked by natural cycles of yin and yang and the five phases. If the emperor did not behave according to proper ritual, ethics, and morals, he could disrupt the fine balance of these cosmological cycles and cause calamities such as earthquakes, floods, droughts, epidemics, and swarms of locusts.
How many realms were commonly thought of as being linked by a natural cycle?
three realms