Lacking light or relating to environments where no light penetrates. In aquatic systems, the aphotic zone lies below the depth where photosynthesis can occur.
From Greek 'a-' meaning 'without' and 'photos' meaning 'light.' The term developed alongside 'photic' in early 20th century marine biology as scientists mapped the vertical distribution of light in oceans and lakes.
The aphotic zone covers 90% of the ocean's volume and is Earth's largest ecosystem, yet it's completely dependent on 'marine snow' - a constant rain of organic particles falling from the sunlit world above! This dark realm hosts incredible diversity, from giant tube worms to bioluminescent deep-sea creatures.
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