Corals derive their astonishing colors, and much of their nourishment, from symbiotic algae that live on their surfaces. The algae photosynthesize and make sugars, which the corals feed on. But when temperatures rise too high, the algae produce too much oxygen, which is toxic in high concentrations, and the corals must eject their algae to survive. Without the algae, the corals turn bone white and begin to starve. If water temperatures soon return to normal, the corals can recruit new algae and recover, but if not, they will die in months.
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Guns arrived in Japan around 1543 with two Portuguese adventurers who stepped ashore, pulled out a gun, and shot a duck on the wings. A Japanese nobleman happened to be there, was very impressed, bought these two guns for $10,000, and had his sword-maker imitate them. Within a decade, Japan had more guns per capita than any other country in the world, and by the year 1600 Japan had the best guns of any country in the world. And then, over the course of the next century, Japan gradually abandoned guns. What happened was that the Samurai, the warrior class in Japan, had been used to fighting by standing up in front of their armies and making a graceful speech, the other opposing Samurai made an answering graceful speech, and then they had one-on-one combat. The Samurai discovered that the peasants with their guns would shoot the Samurai while the Samurai were making their graceful speeches. So the Samurai realized that guns were a danger because they were such an equalizer. The Samurai first restricted the licensing of gun factories to a hundred factories, and then they licensed fewer factories, and then they said that only three factories could repair guns, and then they said that those three factories could make only a hundred guns a year, then ten guns a year, then three guns a year, until by the 1840s when Commodore Perry came to Japan, Japan no longer had any guns. The banning of the guns could work only in isolated Japan, where there were no neighbors as a threat, and where there were no neighbors from whom to reacquire the technology.
As of the year 1400, China had by far the best, the biggest, and the largest number of, ocean-going ships in the world. Between 1405 and 1432 the Chinese sent 7 ocean-going fleets, the so-called treasure fleets, out from China. Those fleets comprised hundreds of ships; they had total crews of 20,000 men; each of those ships dwarfed the tiny ships of Columbus; and those gigantic fleets sailed from China to Indonesia, to India, to Arabia, to the east coast of Africa, and down the east coast of Africa. It looked as if the Chinese were on the verge of rounding the Cape of Good Hope, coming up the west side of Africa, and colonizing Europe. There was a new emperor in China in 1432. In China there had been a Navy faction and an anti-Navy faction. In 1432, with the new emperor, the anti-Navy faction gained ascendancy. The new emperor decided that spending all this money on ships is a waste of money. Okay, there's nothing unusual about that in China; there was also isolationism in the United States in the 1930's, and Britain did not want anything to do with electric lighting until the 1920s. The difference, though, is that this abandoning of fleets in China was final, because China was unified under one emperor. When that one emperor gave the order to dismantle the shipyards and stop sending out the ships, that order applied to all of China, and China's tradition of building ocean-going ships was lost because of the decision by one person. China was a virtual gigantic island, like Tasmania. Now contrast that with what happened with ocean-going fleets in Europe.