The beginnings of modern oceanography lie at the end of the 19th century with oceanic surveys such as that conducted by the British research vessel Challenger. The USA was proposing to explore the Atlantic and Pacific oceans, with Alexandre Agassiz (1835-1910) as joint leader, and German and Swedish ships, too were venturing into the Atlantic. The British government was persuaded to support the Challenger expedition to uphold Britain's international prestige. It was hoped that Challenger’s exploration would be able to answer pressing questions of the day. Was the deep ocean populated with living creatures? Could ocean currents be measured to confirm theories about how oceanic waters circulated? If sediment lay on the ocean floor, would it be the familiar chalk? Challenger was able to answer some of these questions, but the oceanic circulation remained a controversy even at the end of the voyage. It is now known that many variable factors influence the currents. By taking depth soundings, Challenger did discover submarine mountains in the middle of the Atlantic Ocean (pp. 38-39) and found the Mariana Trench, 11,033 m (36,000 ft) down in the Pacific Ocean.