Problem: Chapter IX deals with the fact that the geologic record appears to show forms of life suddenly arising, without the innumerable transitional fossils expected from gradual changes. Darwin borrowed Charles Lyell's argument in Principles of Geology that the record is extremely imperfect as fossilisation is a very rare occurrence, spread over vast periods of time; since few areas had been geologically explored, there could only be fragmentary knowledge of geological formations, and fossil collections were very poor. Evolved local varieties which migrated into a wider area would seem to be the sudden appearance of a new species. Darwin did not expect to be able to reconstruct evolutionary history, but continuing discoveries gave him well founded hope that new finds would occasionally reveal transitional forms. To show that there had been enough time for natural selection to work slowly, he again cited Principles of Geology and other observations based on sedimentation and erosion, including an estimate that erosion of The Weald had taken 300 million years. The initial appearance of entire groups of well developed organisms in the oldest fossil-bearing layers, now known as the Cambrian explosion, posed a problem. Darwin had no doubt that earlier seas had swarmed with living creatures, but stated that he had no satisfactory explanation for the lack of fossils. Fossil evidence of pre-Cambrian life has since been found, extending the history of life back for billions of years.
What is the name of the group of well-developed organisms that were discovered within fossil-bearing layers?
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Answer: the Cambrian explosion


Problem: Ibn Sina's first appointment was that of physician to the emir, Nuh II, who owed him his recovery from a dangerous illness (997). Ibn Sina's chief reward for this service was access to the royal library of the Samanids, well-known patrons of scholarship and scholars. When the library was destroyed by fire not long after, the enemies of Ibn Sina accused him of burning it, in order for ever to conceal the sources of his knowledge. Meanwhile, he assisted his father in his financial labors, but still found time to write some of his earliest works.
Why did some accuse Ibn Sina of burning down the royal library?
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Answer: to conceal the sources of his knowledge


Problem: Beginning in 1939, Dr. Peter Goldmark and his staff at Columbia Records and at CBS Laboratories undertook efforts to address problems of recording and playing back narrow grooves and developing an inexpensive, reliable consumer playback system. It took about eight years of study, except when it was suspended because of World War II. Finally, the 12-inch (30 cm) Long Play (LP) 33 1⁄3 rpm microgroove record album was introduced by the Columbia Record Company at a New York press conference on June 18, 1948.
On what date was the 12 inch LP released?
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Answer:
June 18, 1948