First Woman to Reach Ocean’s Deepest Point Was First to Walk in Space

astronaut kathy sullivan touches down in the mariana trench seven miles beneath the ocean surface

By Jonny Lupsha, Wondrium Staff Writer

Astronaut Kathy Sullivan, the first woman to walk in space, has visited the ocean’s deepest point, Science Alert reported. Now, Sullivan has become the first woman to reach the ocean’s deepest point, seven miles beneath the surface in the Mariana Trench. Life at that depth is cold, dark, and strange.

Mariana Trench 3D rendering
In complete darkness and nearly seven miles below the ocean’s surface, the Mariana Trench has a water temperature just a few degrees above freezing, with a water pressure of eight tons per square inch. Photo by Oliver Denker / Shutterstock

According to Science Alert, Kathy Sullivan’s journey to the ocean’s deepest point, known as Challenger Deep, was incredible. “Challenger Deep lies nearly seven miles (11 kilometres) below the Pacific Ocean’s surface within the Mariana Trench about 200 miles (300 kilometres) southwest of Guam,” the article said. “Sullivan is the eighth person in history to make the dive, according to EYOS Expeditions, the company coordinating the mission. It took four hours to descend to the crushing depth of 35,810 feet (10,941 metres).”

Under such heavy water pressure, where light never penetrates, it can be difficult to imagine any creature surviving. Life in the deep is as mysterious as it is fascinating.

Mermaids, Krakens, Cthulhu Not Found

The Merriam-Webster Dictionary tells us that the term “benthic” means “of, or relating to, or occurring at the bottom of a body of water,” and can also carry the looser definition “of, or relating to, or occurring at the depths of the ocean.” This helpful term defines much of the ecology at the sea floor.

“The organisms that exist down there mostly do move and grow slowly,” said Professor Harold J. Tobin, Professor of Geoscience at the University of Wisconsin-Madison. “Starting from the 1960s when scientists got a little bit more sophisticated about how they sampled that benthic fauna, it was discovered that there were surprisingly diverse life forms and robust ecosystems, even if the actual total biomass is relatively small on the deep sea bed.

“It’s far from a desert in the sense of having diverse life.”

Professor Tobin said that a tool called the epibenthic sled trawls deep sea floors, scoops into them, and pulls up matter both on the floor and just above it for oceanographers to inspect. He said it was first used in a slightly shallower ocean area called an abyssal plain. When it returned to the surface, each “toe” of the epibenthic sled contained “literally hundreds of species” and between thousands and tens of thousands of individual organisms.

Real Creatures of the Deep

One organism that lives in the deepest parts of the ocean is the bristle worm, Professor Tobin said, but it also lives in the mid-ocean ridges in abundance. Other creatures are plentiful at the bottom of the sea.

“Another type of worm that lives down there, a little bit more complicated organism, is called an acorn worm,” Professor Tobin said. “That forms a U-shaped tube in the seabed and basically just eats its way through the sediment, taking in all the mud and sand, digesting every bit of organic material that’s in it and then expelling what’s left out behind into these convoluted-looking worm castings that cover large parts of the sea floor.”

Aside from bristle worms and acorn worms, holothurians—also known as sea cucumbers—are plentiful in the deep. Sea cucumbers are part of a phylum called echinoderms, which dominate the sea floor.

“There are many thousands of different species of echinoderms,” Professor Tobin said. “Echinoderm literally means ‘spiny skin,’ so when we think of a sea urchin, we think of an echinoderm. If you remember what a sea urchin looks like, they tend to be circular with pentagonal symmetry, a five-pointed body plan and a central mouth and an anus to expel food waste.”

According to Professor Tobin, echinoderms are the largest phylum of living creatures with no representatives on land or in fresh water. Their sheer numbers make them the kings of the deep.

Much of the ocean remains unexplored. Kathy Sullivan’s journey to the deepest point of the Mariana Trench can be considered one small step in discovering it—or maybe a giant leap?

Dr. Harold J. Tobin

Professor Harold J. Tobin contributed to this article. Professor Tobin is Professor of Geoscience at the University of Wisconsin-Madison. He earned his BS in Geology and Geophysics from Yale University and his PhD in Earth Sciences from the University of California, Santa Cruz.