In Our Time: The Mariana Trench

This episode of 'In Our Time' explores the Mariana Trench, the deepest known point on Earth, delving into its geological formation, discovery history, and the extreme life that survives in its crushing depths. Host Misha Glennie is joined by oceanographers Alan Jameson, John Copley, and Heather Stewart, who share their firsthand experiences diving into the trench using submersibles. They explain how tectonic plate subduction creates the trench, describe the challenges of deep-sea exploration—including communication, pressure, and tracking—and reveal the surprising resilience of deep-sea organisms like the snailfish and the unique anemone Galathianthymum. The discussion also confronts the environmental toll of human activity, with evidence of plastic waste, discarded fiber-optic cables, and even a crashed SR-71 Blackbird found in the trench. The guests emphasize that while the Mariana Trench is the most prestigious deep-sea site, it’s not representative of all trenches, and other regions like the Kermadec Trench offer richer geological insights. The episode concludes with reflections on the interdisciplinary nature of deep-sea research and the profound implications of climate change on deep-ocean oxygen levels. Key takeaways include: 1) The Mariana Trench is formed by subduction of the Pacific Plate, not by a single event but over millions of years; 2) Life in the hadal zone thrives through adaptations at the molecular level, not just physical resilience; 3) Human pollution has reached even the deepest oceanic trenches, with plastic and discarded technology now common; 4) The trench is not a typical environment—its isolation and lack of surface input make it an outlier; 5) Scientific exploration requires collaboration across geology, engineering, biology, and oceanography; 6) Climate change is already altering deep-ocean oxygen levels, with impacts expected in centuries; 7) The Mariana Trench’s fame overshadows other equally important deep-sea environments; 8) In-situ preservation techniques are revolutionizing how we study deep-sea biology without bringing specimens to the surface.