Before the development of science and technology, man viewed the natural world as mysterious and sometimes frightening. People were confounded by questions such as What is thunder? How are mountains formed? What causes sickness? Then, with the development of science, man started to find the answer to such questions.Now that we live in an age of advanced scientific knowledge, it sometimes seems we have unlocked all the mysteries of nature. Yet every so often, nature presents us with unexplained phenomena for which there are still no rational, scientific explanations.