image taken near a reef

The Ocean Floor: An Alien World on Earth

March 16, 2023 - Ellie Poverly

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What would life be like in a world with no sunlight? Thousands of species have evolved on the ocean floor, in depths and temperatures no human could survive. These marine creatures go their whole lives without sunlight. Some are microscopically small while others are infamously gigantic. The ocean floor is a strange but incredible place that can teach us a lot about how life formed on Earth, and what life might be like on other worlds. 

The Ocean Floor: A Strange World

The ocean might seem like a flat expanse of water from the surface, but there is a dynamic world beneath the waves. The geography of the ocean floor is just as complex and varied as geography on dry land. There are several types of landforms found underwater, ranging from shallow continental shelves to ocean trenches reaching over 30,000 feet below sea level. 

Most features of the ocean floor are not visible from the surface. Humans mainly interact with beaches, coastlines and the tips of underwater mountains and volcanoes. Few people venture further than the edges of continental shelves. 

Marine life is most commonly found at these higher depths, as well. Closer to the surface, ocean life has more access to natural light, which many species rely on, particularly plant life. This creates ideal conditions for natural food chains like those found on dry land. 

Deep sea begins with the “twilight zone”, expanses of ocean 650 to 3,300 feet deep. In this depth, life gets very little sunlight, although some rays still break through. It isn’t just dark in the twilight zone – at this depth, temperatures are extremely low and water pressure gets increasingly high. 

Going even deeper, the “midnight zone” extends from 3,300 feet to 13,000 feet below the surface. No sunlight reaches this depth, creating a world completely in the dark. The area even deeper than the midnight zone is known as the Abyss, which roughly encompasses terrain from 13,000 feet deep to the bottom of the ocean floor. 

Oceanic trenches are sometimes considered their own unique category. The deepest trench in the world is the Mariana Trench in the Pacific Ocean, which scientists estimate is 35,875 feet deep. This particular area is also known as “Challenger Deep”. 

Life on the Ocean Floor

Lack of sunlight doesn’t stop life from forming. The ocean floor is a geologically dynamic place. Features like fissures and hydrothermal vents can provide nutrients to life underwater where sunlight cannot reach. In fact, scientists estimate that 25% of all life on Earth lives in the deep ocean, but 91% of these species remain undiscovered. 

Life on the ocean floor develops very differently from life near the ocean’s surface. High pressures and low temperatures create an unusual environment for evolution to occur. This means different traits are advantageous for deep sea life compared to surface life. For example, many marine organisms found in the twilight zone are invertebrates like cephalopods, a group of animals that includes squids and octopi. 

One famous example of deep sea life is the giant squid, which can be over 40 feet long. These enormous squids live in twilight zone ocean regions all over the world. They’ve long been a staple of science fiction due to their unusually gigantic size. Colossal squids are even larger cousins of the giant squid, reaching lengths over 50 feet. They are extremely rare, though, so little is known about them. 

Deep Sea Gigantism

Both of these squids are examples of a phenomenon known as deep sea gigantism. Despite intense pressures of hundreds of atmospheres in the deep seas, many species are able to grow to enormous proportions. This trend is particularly common among invertebrates, such as cephalopods like the giant squid. 

Scientists believe that the extremely low temperatures at the ocean floor make gigantic size advantageous for marine life. Larger animals can move more efficiently and slow down metabolic processes, which is helpful when food is difficult to find like it is on the ocean floor. A lack of more aggressive predators like humans may also play a role in deep sea gigantism, particularly for species that don’t move at all, like giant sponges. 

Bioluminescence: Lighting the Ocean Floor

Another trait commonly found in deep sea life is bioluminescence. While sunlight may not reach the deep seas, many creatures are able to create their own light. Bioluminescence occurs through chemical reactions that create visible radiation. Luciferin is the chemical compound responsible for creating light, but photoprotein or luciferase is required to actually create the light-emitting reaction. 

Creatures with bioluminescent features are able to create these chemical compounds naturally in their bodies. They may use the natural light to lure in prey, confuse predators or communicate with one another. 

One of the most famous types of bioluminescent animals is the anglerfish. This is a family of eerie looking fish best known for the bioluminescent lure that grows out of their heads, used to attract prey. An anglerfish famously made an appearance in the Pixar movie Finding Nemo, although fish like Marlin and Dory wouldn’t be able to survive in the midnight zone where anglerfish live. 

Similarities to Other Planets and Moons

Exploring the ocean floor is important for a number of reasons. Not only does it hold valuable resources, but there are also countless species waiting to be discovered in the deep seas. This undiscovered marine life is interesting for purely scientific reasons but could also provide insights for new medical treatments and conservation research. 

The ocean floor can also give us a glimpse of what life might be like on other worlds. Water is one of the most important factors in the development of life on Earth. So, scientists often start by looking for water when searching for signs of life beyond our planet. Life on the ocean floor could demonstrate how life on aquatic worlds could develop. 

There are two moons in our solar system scientists believe could hold alien life: Europa, a moon of Jupiter, and Enceladus, a moon of Saturn. Both moons have icy crusts with suspected liquid water beneath. In fact, probes passing Enceladus have even sampled liquid water plumes breaking through the ice that contain organic molecules. 

Both of these suspected ocean worlds present striking similarities to Earth’s deep oceans. Life on Europa or Enceladus would experience no sunlight. All nutrients would be derived from underwater hydrothermal vents or subsurface vents. These fissures would provide heat and the elements vital to the evolution of life. Deep sea life on Earth also evolves in unusual pressures, which could shed light on how gravity impacts the development of ocean life. 

Studying life on the ocean floor of Earth can help us understand how life might develop on worlds like Europa and Enceladus. This gives scientists some foundational knowledge of what to expect and what to search for when looking for signs of life on these alien aquatic worlds. 

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Author

Ellie Poverly

Ellie Poverly is a science writer specializing in astronomy and environmental science and is the Associate Editor of Revolutionized. Ellie's love of science stems from reading Richard Dawkins books and her favorite science magazine as a child, where she fell in love with the experiments included in each edition

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