We sometimes hear that ‘we know more about Mars than the deep ocean’, but is that true? Exploring the deep ocean is a recent enterprise, made possible by new technology in the past two centuries, but what we now know about the dark depths is as remarkable as the unknowns that remain.
This lecture examines the deep-sea discoveries that have transformed our understanding of our planet, and the history of exploring the deep ocean that covers most of it.

Dr Jonathan Copley is Associate Professor in Ocean Exploration and Public Engagement (part-time) within Ocean and Earth Science, National Oceanography Centre Southampton at the University of Southampton. In June 2013, he became the first British person to dive more than 5 km deep in the ocean, taking part in the first dive by a human-occupied vehicle to the world's deepest known hydrothermal vents. In December 2016, he took part in the first dives by human-occupied vehicles to 1 km deep in the Antarctic, during filming of the BBC's Blue Planet 2 series.