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SYFY WIRE Science Behind the Fiction

Could Underwater's monsters really exist deep in the Mariana Trench?

By Cassidy Ward
Underwater Poster

It's a shame we don't have more movies that take place underwater. The deep seas hold the same sort of mystery and potential for horror as deep space — but unlike with space, we know the oceans are teeming with life. William Eubanks' recent blockbuster, Underwater, leans into these innate sea-faring fears, hard.

The story progression is relatively simple: Kristen Stewart and the rest of her small crew is trapped at the bottom of the Mariana Trench. Their safe haven is no longer hospitable, and they have to reach the safety of a nearby facility before time runs out. This, in and of itself, should be enough to keep the tension high, but the filmmakers dial it up to eleven by adding monsters. If the lack of oxygen and immense pressure don't kill you, never you mind, there are things with teeth and claws in the deep.

Underwater does a lot of things right, in terms of tapping into the things that scare us. Darkness, claustrophobia, isolation, the lack of regular day/night rhythms, and most importantly, the unknown. Add in a disaster, the loss of the one thing separating you from all the death and destruction beyond the station walls, and you've got a perfect slurry for fear, even before the monsters show up.

But, of course there are monsters. This hearkens back to some of our earliest stories, creatures from the deep rising from their hiding places to swallow ships whole, dragging their crews into the murky depths. It's the Kraken and the Bermuda Triangle all rolled into one, set in the deepest depths of the ocean.


The Mariana Trench is the deepest underwater place there is. Its deepest point, Challenger Deep, reaches to a depth of nearly 11,000 meters (36,000 feet or nearly 7 miles). To put that in context, the average ocean depth is 12,000 feet, only a third of the Trench. It's so deep that if you were to submerge Mt. Everest, the world's highest point, at the bottom, its peak would remain more than a mile underwater. Even the world's true tallest mountain, the partially submerged Mauna Kea (33,000 feet) would be unable to reach the surface from that depth.

Four crewed descents down into the Trench have taken place, the earliest of which occurred in 1960 with Don Walsh and Jacques Piccard. The most recent descent took place last year, embarked upon by Victor Vescovo in April, and then again in May, making him the first person to dive Challenger Deep twice.

These expeditions, both crewed and uncrewed, have revealed some interesting things about Earth's deepest locale, most impressively, the life there.

Despite its immense distance from everywhere else, life seems to be abundant in the Trench. Recent expeditions have found myriad creatures living out their lives at the bottom of the sea-floor. Xenophyophores, amphipods, and holothurians (not the names of alien species, I promise) all call the trench home. And while some of them live on traditional food, plants, and animal that find their way there, others are dependent on chemical nourishment from the earth, itself.

Perhaps the most impressive, among all the life in Challenger Deep, are the xenophyophores. These microbes are single-celled, but their widths are measured in inches.

That's incredibly large for a single-celled organism, to say the least. Most of the time you'd need a microscope to see a single cell, but these creatures are large enough for you to trip over.

If you were to fill up the space of one of these creatures with average-sized human cells, you'd need about 100 billion of them.

These unassuming creatures are just one example of…


There seems to be a trend among creatures living at incredible depths: they're large, especially compared to similar life-forms at shallow depths. In addition to the baseball-sized xenophyophores, the ocean floor is home to a number of animals that tower over their more familiar relatives.

Giant isopods share a similar body plan with the common pill bug. Without any context, you might easily assume they were close relatives, and you wouldn't be wrong. The difference is, while pill bugs can easily fit on a fingertip, these sea-dwelling crustaceans are about a foot long.

Similarly, giant squids share a body plan and are related to more common squid, but they are large enough to have inspired horror stories for centuries.

All of this owes to an interesting phenomenon that happens in isolated environments like the ocean depths.

Biologist Craig R. McClain, in a 2006 study, equated deep-sea environments to those of remote islands. Gigantism also commonly occurs on islands, as a result of diminished resources. One explanation is that life which finds itself isolated in a smaller environment, with fewer available resources, trends toward larger body plans which can more easily handle periods of famine. Another possible explanation is that animals with fewer predators tend to grow larger.

What's indisputable is that earlier life, common ancestors of creatures we see on land or at shallower depths, found themselves in the deep and, over time, grew to incredible sizes.

Whatever the cause, one thing is certain, the depths are filled with immense and somewhat familiar creatures.

All of which causes one to wonder…


To date, we've only explored about 5 percent of the world's oceans. From a certain point of view, we know more about distant locales in our solar system than we do about the most abundant environments here at home.

For all of human history we've been searching, whether we want to admit it or not, for the monsters which haunt our nightmares. And we've never found them. But maybe that's because once discovered, they cease to be monsters.

There is no functional difference between a sasquatch and a gorilla, except that we've defined and categorized gorillas, placed them neatly in their position among the web of natural life. Once done, they cease to be mysterious. They cease to be monsters.

A Kraken is only a Kraken until it's a giant squid. No longer a sea monster, now something to learn about.

It seems incredibly likely there are uncountable numbers of creatures living in the depths. And some of them are monstrous, just take a few minutes to gaze upon a ghost shark and tell yourself you wouldn't die of shock if you encountered one while walking across Challenger Deep. How about this 12-foot crab with rending claws and a face like a bed of nails?

Exploration is the defining characteristic of humanity, and we should embark into that vast ocean abyss with open hearts and minds, and every bit of enthusiasm we can muster. But we should probably be just a little bit afraid. Because, as we all know, when you stare into the abyss, well…

Underwater is in theaters now.