It was a British geologist who in the early 1920s discovered
that Stonehenge, the mysterious circle of rough-hewn monuments
in southern England, was roughly 4,000 years oldfar older than
previously thought. He also showed that the stones themselves
had been hauled from a great distance200 miles (321.8
kilometers) from a quarry in western Wales. Later in the 20th
century revolutionary dating methods have revealed the ages of
artifacts with increasing precision. Satellites and related
technology, such as ground-penetrating radar, have helped locate
likely sites of human habitation. Technology has also opened up
an entirely new realm: the sea. In the early 1940s Frenchmen
Jacques-Yves Cousteau and Émile Gagnan co-invented the Aqua-Lung
(known today as scubaself-contained underwater breathing
apparatus). Anthropologist George Bass and historian Peter
Throckmorton in the early 1960s began using this gear to explore
ancient shipwrecks in the Mediterranean. The late 20th century
saw the development of a new generati