1In this final lecture, we descend to the hadal zone, the deepest region of the ocean, lying below six thousand metres.
2What I want to emphasize at the outset is that hadal trenches remain less explored than the surface of the Moon.
3Contrary to the long-held assumption that extreme pressure precludes complex life, these trenches support surprisingly rich biological communities.
4The first crewed descent reached the deepest point in nineteen sixty, yet decades passed before anyone returned there.
5It was not a lack of scientific interest but rather the prohibitive engineering costs that delayed these return expeditions.
6Organisms living at such extraordinary depths produce specialised molecules called piezolytes, which stabilise their delicate proteins against the crushing pressure.
7The initial survey suggested fish could not survive below eight thousand metres, though subsequent footage overturned that limit.
8Let me give you a concrete example: the snailfish, whose partially transparent body lacks the rigid structures that pressure would destroy.
9Moving on to the technology, modern landers can remain on the seabed for months, recording behaviour without any human disturbance.
10Perhaps most troubling, even these remote depths contain microplastics, demonstrating that no corner of the ocean remains untouched.
11To conclude, the hadal zone challenges our definition of habitability and continues to reward every expedition with unexpected discoveries.