In 2003, a fisherman in Chetumal Bay, Mexico, noticed a grouper disappear beneath the surface and later found a hidden opening in the water. More than a decade later, his son guided researchers back to the site. Initial measurements found no bottom at 425 feet, and instruments recorded warm, salty water and rising currents where they were not expected. The hole, known as Taam Ja’, has since been measured to at least 1,372 feet deep, making it the deepest known blue hole on Earth.

Blue holes are essentially ancient sinkholes that filled with water as sea levels rose. They appear as dark circular shadows from above because of their depth. Taam Ja’ is unusual because it is difficult to spot from the surface, unlike more famous examples such as the Great Blue Hole in Belize.

In December 2023, researchers lowered a conductivity, temperature, and depth profiler into the hole. At around 1,312 feet, the water became warmer and saltier, with readings matching the open Caribbean Sea. This was surprising because the hole is located far inside the bay and appears horizontally isolated from the open ocean. The finding suggests the existence of subterranean tunnels or fractures connecting the hole to open seawater beneath the rock.

The region’s geology may explain this. Taam Ja’ is near the Chicxulub crater, the site of the asteroid impact about 66 million years ago that is widely linked to the extinction of the dinosaurs. The impact may have fractured the underlying rock, potentially making it easier for caves, tunnels, and blue holes to form in the area.

During an early expedition, researchers observed that the water above Taam Ja’ was calm while the rest of the bay had waves. From the center of the hole, water slowly rose upward, like a gentle spring. This occurred only once, and the behavior made diving conditions intimidating for those involved.

The deep, dark, and isolated environment raises questions about what might live there. Scientists consider it unlikely that large creatures could survive in such conditions, but microscopic life may exist. Any organisms found would likely be ancient and adapted to extreme environments. Their presence could have implications for understanding how life might survive on other worlds, such as the moons Europa or Enceladus.

Recreational divers cannot explore Taam Ja’. Standard scuba equipment only allows for depths of about 130 feet, and even professional divers rarely exceed 1,000 feet. The pressure at such depths requires specialized equipment and training. The next step is likely to send a remotely operated vehicle, or ROV, equipped with cameras and sensors.

The interior of the hole may contain side tunnels, ledges, or other features that make depth readings difficult. Scientists note that more of the ocean floor has been mapped than the interior of the Earth. Still, Taam Ja’ holds the record as the world’s deepest known blue hole for now.

Separately, a recent study from Virginia Tech examined a different kind of ground movement in the United States. The research found that land subsidence, the gradual sinking of the ground, is affecting 28 major US cities. This sinking is caused largely by the removal of groundwater, which leaves underground reserves depleted and the land above them unsupported.

New York, Dallas, Seattle, and other cities are sinking at rates of a few millimeters per year. This may sound small, but the ground sinks unevenly. If one part of a building or road sinks faster than another, the structure can become damaged. More than 29,000 buildings are located in zones considered at high or very high risk of damage.

Houston is sinking at about 5 millimeters per year, roughly twice as fast as New York. Parts of California have seen the ground drop by nearly 30 feet in some areas, causing large depressions and infrastructure problems. The problem is most severe where groundwater is heavily extracted, such as in agricultural regions of California.

Authorities have proposed solutions such as wastewater recycling and rainwater harvesting. Treating and reusing wastewater could reduce the need for groundwater, while creating green zones in cities could help absorb rainwater and return it to underground sources. These approaches would not stop the process overnight, but they could slow it down.