The asthenosphere, as described in Brian Kevin’s Yellowstone and Grand Tetons National Parks guide (Bookshop|Amazon) is a gurgling sea of plasticized rock beneath the earth’s rocky crust. Asthenosphere derives from Greek asthenes, meaning “weak” or “feeble,” and a relative of the English words for “muscle weakness,” myasthenia, and “nerve weakness,” neurasthenia. The Greek word for “strong,” sthenos, gives us the English word calisthenics, or “beautiful strength,” a form of exercise originally designed primarily to promote strength and fitness in girls. These rhythmic exercises were popularized in the 19th century by the sister of Harriet Beecher Stowe, author of Uncle Tom’s Cabin (Bookshop|Amazon). This is part of a complete episode.