Discovering the "living fossils" of the Atacama Trench

An exploration expedition to the Atacama Trench, in waters north of Chile, between 2,900 and 4,450 metres deep, has revealed benthic ecosystems containing organisms believed to be descendants of those that became extinct 65 million years ago.

The expedition is the work of an international team of scientists, led by researchers from the Centre for Astrobiology (CAB), a joint centre of the Spanish National Research Council (CSIC) and the National Institute of Aerospace Technology (INTA).

The oceanographic expedition was called “Unveiling the Living-Fossil Ecosystems of the Atacama Trench” and took place between May 30 and June 7, 2024, in marine waters off the Atacama Desert in northern Chile. The purpose of the expedition was to search for ecosystems at the bottom of the sea up to 4,450 meters deep, composed of so-called “living fossils”.

Thanks to a project obtained and led by Armando Azúa-Bustos, a researcher from the Department of Planetology and Habitability of the CAB, the group of researchers had exclusive access during those days to the oceanographic research vessel RV Falkor, owned by the Schmidt Oceanographic Institute in the United States.

Using the most advanced underwater research technologies, including the SuBastian robot, this expedition made a true journey back in time and its researchers were able to observe the seabed as it must have been 65 million years ago.

The Atacama Desert in northern Chile is the driest desert on Earth. At 150 million years old, it is also the oldest, or one of the oldest.

Previous findings by Azua-Bustos reported very ancient microorganisms in the coastal mountain range of this desert, whose points of origin were suspected to be in the Pacific Ocean, leading to the question of what other, equally ancient, life forms could be found on the ocean floor off Chile. Additionally, fossils of marine organisms such as brachiopods, crinoids and chitons were already well known in the hyperarid valleys of the Atacama, allowing the suggestion that the ocean floor could contain entire ecosystems from the Jurassic era.

“It was, as the well-known saying goes, like looking for a needle in a haystack,” said Azua Bustos. “We had the vastness of the Pacific Ocean before us and, although we had the most modern oceanographic exploration technologies, we were looking for organisms that were at best a few centimetres in size.”

“However, shortly after the first dive began, they were there,” said Javier Sánchez España, a CAB researcher and participant in the expedition, who will study the minerals formed by microbial activity in the environment found. This supported the hypothesis that very old benthic ecosystems could be found in this little-explored region.

Some of the animals found on the seabed off the Atacama Desert in northern Chile. (Photos: Schmidt Ocean Institute)

Using bathymetry and radar data taken by Falkor, the team has discovered the northernmost and deepest cold seeps in all of Chile, along with their associated ecosystems. These seeps of hydrocarbon-rich fluids are systems conducive to the proliferation of life in extreme conditions, even in the absence of light. “From another point of view, it was like exploring the oceans that we could find on the icy moons of the solar system, moons like Enceladus and Europa,” says Daniel Carrizo, a CAB researcher who will search for molecules produced by life and that could be sought as biosignatures in habitable environments outside of Earth.

Additionally, 70 other species were found living on the seabed, many of them unknown to the expedition’s researchers, who will try to identify and study these species in the future.

“If we were able to find organisms that we suspect are very old, we also expect to find that the microorganisms in these ecosystems are just as old. And if these organisms and microorganisms are very old, perhaps the viruses they contain are also very old,” says Azua-Bustos.

The international team of scientists will now examine each collected sample in detail using a wide range of cutting-edge technologies in order to assess its evolutionary age and, in this way, characterise what is suspected to be one of the oldest deep-sea environments on Earth. Exploring the Earth’s ocean depths will help to better understand the subsurface oceans of Europa and Enceladus, which could provide revealing data on the potential for life beyond our planet, linking the mysteries of our deep seas with those of these distant icy moons. (Source: CAB / CSIC / INTA)