In July 2011, a research team from the Scripps Institution of Oceanography at UC San Diego, working with engineers from National Geographic, deployed several free-falling camera systems into the Sirena Deep section of the Mariana Trench. The cameras recorded video at a depth of 10,641 meters, about 34,911 feet, confirming the presence of giant single-celled organisms called xenophyophores on the seafloor.

The expedition was led by Doug Bartlett, a marine microbiologist at Scripps, alongside Lisa Levin, a deep-sea biologist and director of the Center for Marine Biodiversity and Conservation. Instead of using a single expensive manned submersible, the team deployed multiple baited camera landers simultaneously. These devices, built by National Geographic engineers Eric Berkenpas and Graham Wilhelm, are sturdy frames fitted with high-definition cameras and lights enclosed in thick glass spheres. Weights carry them to the ocean floor, where they record for a set period before the weights are released and the cameras float back to the surface.

The strategy allowed the team to survey more of the Sirena Deep than would have been possible with a single vehicle. The footage showed xenophyophores, a type of giant protozoan that can grow to more than four inches in diameter. Most single-celled organisms are microscopic, making these specimens roughly ten thousand times larger than an average single cell. They achieve this size by containing many nuclei within one continuous cell, and they build protective outer shells, called tests, by gathering and cementing particles from the seafloor.

The discovery set a new depth record for confirmed xenophyophores, previously documented at about 7,500 meters in the New Hebrides Trench. The same expedition also recorded what researchers described at the time as the deepest jellyfish ever observed. Both findings were published through official Scripps research communications and reported by National Geographic.

Bartlett described the find as opening up an entirely new habitat for study, noting its biodiversity and potential biotechnology applications. Levin described the organisms as a rare example of life found exclusively in the deep sea, notable for how well adapted and fragile they are. The researchers also noted that as human activity in deep waters increases, understanding and protecting such organisms becomes more urgent.

Xenophyophores have been studied by scientists since at least 1882, when oceanographer John Murray described a related species found off the coast of Ireland. Their biology remains difficult to study because their delicate, particle-built shells are often destroyed during collection. Most of what researchers know about living xenophyophores comes from remote camera observation rather than physical sampling.

The organisms have a documented ability to concentrate heavy metals, including lead, uranium, and mercury, within their bodies. This natural filtering capacity makes them unusually resistant to materials that would be toxic to most other life forms, and it has drawn interest from researchers studying how life survives in extreme environments.

The 2011 expedition found xenophyophores at approximately the four hundred meter mark within the deepest quarter of the Mariana Trench. The depth is close to the physical limit for vertebrate life, which faces biochemical constraints related to pressure. Xenophyophores, lacking bones, muscles, and complex internal organs, do not face this same biological ceiling.

Since 2011, researchers have continued to document deep-sea ecosystems, including chemosynthetic communities of tubeworms and clams, snailfish with flexible skeletons, and scavenging crustaceans that subsist on organic material drifting down from above. Studies of xenophyophores have continued, focusing on how they distribute themselves across trench systems and what role they play in supporting other small creatures that live within or around their structures.

The scientific response to the 2011 discovery was not confusion but a straightforward explanation of what had been found and why it mattered. Bartlett and Levin both spoke publicly and specifically about the discovery, describing it as an opportunity for further study. Scripps issued official communications about the findings, and National Geographic covered the expedition independently.

The depth figure commonly cited in viral retellings, 35,000 feet, is closely consistent with the recorded measurement of 34,911 feet. The deeper point of the discovery is that a single-celled organism can grow to an unusual size at extreme depths. That fact has been documented, explained, and studied in detail since the footage was first collected.