The Timeline: Deep-sea exploration

700s: Sounding weights

Viking sailors used sounding weights – weights made from lead with a hollow bottom attached to a line – to measure the depth of the sea and to collect samples from the seabed. After the sounding weight had reached the bottom, it would be pulled up, and the line would be measured in fathoms and duly recorded.

1620: The first submarine

A Dutch architect, Cornelius Drebbel, is credited with building the very first submarine. Made from a wooden frame and covered in animal skin, the submersible could travel underwater at 15 feet, and was propelled along by oars that were sealed with leather flaps. Drebbel test-drove the submarine down the river Thames.

1700s: Science and the sea

Modern deep-sea exploration based on science is said to have begun when the French scientist Pierre-Simon Laplace calculated the depth of the Atlantic Ocean from observing the tidal motions along the shores of West Africa and Brazil. He estimated the average depth to be 13,000 feet, which scientists using sounding management later proved to be accurate.

1872-76: Life in the deep

The British launched their first expedition to explore solely the deep ocean by sending out the HMS Challenger, a laboratory ship, on a four-year expedition that covered nearly 70,000 nautical miles. It discovered 4,417 new species of marine organisms and collected hundreds of samples and measurements. It was on this trip that the first view of major sea-floor features such as the deep ocean basis was obtained.

1960: The deepest point

Jacques Piccard and Don Walsh were the first humans to reach the deepest part of the ocean, a point in the 6.8-mile-deep Mariana Trench in the western Pacific Ocean, called the Challenger Deep. It took them five hours in their steel submersible, the Trieste, to descend into the trench on the perilous expedition.

2011: Return to the trench

Scientists probe the Mariana Trench using a modern submersible and find that ocean trenches play a larger role in regulating the Earth's chemistry and climate than was previously thought after discovering that the trenches act as carbon sinks, meaning the sea can capture carbon dioxide in the global carbon cycle. The film director James Cameron announces he is building a submersible to allow him to film in the trench, to gather footage for a sequel to Avatar.