Hadal:
The hadal zone is the ocean region extending from 6,000 meters (19,685 feet) down to the bottom of the deepest trenches, which can reach nearly 11,000 meters (36,089 feet). These depths are found exclusively within long, narrow submarine canyons formed where one of Earth’s tectonic plates subducts beneath another. The combined area of all these trenches is roughly the size of Australia.
Life in this zone must withstand hydrostatic pressure that can exceed 1,000 times the standard atmospheric pressure at sea level. This pressure is equivalent to about 100 elephants standing on a dinner plate.
Beyond the pressure, the hadal environment is characterized by perpetual darkness, as sunlight cannot penetrate these depths. The only light is produced by bioluminescent organisms. Water temperatures are consistently just above freezing, typically ranging from 1°C to 4°C, due to the lack of solar heating. [Biology Insights]
Noted in “How life thrives in one of the most hostile environments on Earth,” James Woodford, NewScientist (9 August 2025, paywall):
[Mengran Du at the Chinese Academy of Sciences in Sanya] and her colleagues completed 24 dives in a crewed submersible between 8 July and 17 August 2024, exploring 2500 kilometres of the Kuril-Kamchatka Trench and western parts of the Aleutian Trench, at depths ranging from 5800 to 9533 metres. The hadal zone, a near-freezing area more than 6000 metres deep, is devoid of light and has crushing pressure.
The life there is called the hadal biosphere. It survives by either harvesting energy from nutrients that descend from the surface, which were created via photosynthesis, or by chemosynthesis, where chemicals are the energy source.
