The deep sea refers to the part of the ocean below 200 meters (656 ft.), at which light begins to disappear. Despite making up more than 90% of the Earth’s marine environment, much of the deep-sea ecosystems is still a question mark for researchers.

Human eyes have only seen a tiny, tiny, tiny fraction of the areas of the world that are covered by deep water. Scientists want to change how they explore these regions.

In a new study published in Science Advances, oceans researchers say that just 0.001% of the deep seafloor has been visually observed. The findings highlight the potential for a lack of understanding of ocean biodiversity.