Only a scattering of light penetrates the deep water, more than 300 feet beneath the ocean surface off the coast of Guam. It’s like twilight to the human eye, even in the middle of the day.

This part of the ocean, known as the upper twilight zone, is one of the least explored ecosystems on Earth because it’s so difficult, expensive and dangerous to reach. It’s only accessible by submarine, remotely-operated vehicle or by specially trained technical divers.

But humans are starting to unravel the mysteries of life here. In November, a group of scientific divers from the California Academy of Sciences successfully navigated a series of perilously deep dives.

Their mission was to fetch monitoring devices lodged in Guam’s deep reefs that have been collecting data on marine life and ocean temperatures for more than eight years.

Image: Mathieu Turle, Unsplash