Explorers of the Deep Sea

Welcome to the Deep

More than half of our planet is covered by ocean, and most of it is deeper than you might imagine. If you stood at the surface of the sea and looked down, you would not be able to see the bottom. In the deepest parts, the ocean floor is almost 11 kilometres below the waves — deeper than the tallest mountain is high!

This dark, cold, mysterious place is called the deep sea. Let's explore it together.

A World Without Sunlight

Sunlight can only shine down through the very top layer of the ocean. Below about 200 metres, the water starts to get dark. Below 1,000 metres, it is pitch black, all the time. There is no day and no night down there — just endless dark.

The deep sea is also very cold, close to freezing, and the weight of all the water above pushes down with enormous pressure. If you went down without protection, the pressure would crush you. That is why exploring the deep sea is so hard, and so exciting.

Animals That Make Their Own Light

How can anything live where it is so dark? Many deep-sea animals have a clever trick: they make their own light. This glowing is called bioluminescence.

The famous anglerfish has a little glowing lure that dangles in front of its mouth like a fishing rod. Smaller fish swim toward the light out of curiosity — and become the anglerfish's dinner.

Some jellyfish flash blue light to scare off enemies. Some squid squirt glowing clouds instead of dark ink. In the deep sea, light is not just pretty — it helps animals hunt, hide, and find each other.

Giants of the Deep

The deep sea is home to some surprisingly large creatures. The giant squid can grow longer than a school bus, with eyes as big as dinner plates — the largest eyes of any animal on Earth. Those huge eyes help it spot the faint glow of prey in the darkness.

There is also the colossal squid, which is even heavier, and strange-looking fish like the gulper eel, which can open its mouth wide enough to swallow prey bigger than itself.

For a long time, no one had ever seen a living giant squid in its home. People only found pieces washed up on beaches. It was not until cameras were sent deep underwater that scientists finally filmed one alive.

How We Explore the Deep

People cannot swim to the deep sea, so explorers use special machines.

A submersible is a small submarine built to dive very deep. Its walls are thick and strong so the pressure cannot crush it, and it carries bright lights and cameras. A few brave explorers have ridden submersibles all the way to the deepest spot in the ocean.

Even more often, scientists use ROVs — remotely operated vehicles. These are underwater robots controlled from a ship by a long cable. The robot's cameras send pictures back up, so scientists can explore without ever leaving the boat. Robots can stay down longer and go to places that would be too dangerous for people.

Mountains and Vents on the Seafloor

The bottom of the ocean is not flat and empty. It has towering mountains, deep canyons, and wide plains. In some places, hot water gushes out of cracks in the seafloor. These are called hydrothermal vents.

The water from a vent can be hotter than boiling, and it is full of minerals. Amazingly, whole communities of animals live around these vents — strange tube worms, ghostly white crabs, and clams — even though there is no sunlight at all. They survive on energy from the chemicals in the vent water. Scientists were astonished when they first discovered this hidden world.

Why It Matters

The deep sea is the largest living space on our planet, and we have explored only a small part of it. New creatures are discovered there almost every time scientists go down. Some deep-sea animals may even help us make new medicines one day.

The ocean also helps keep our whole planet healthy, so protecting it matters for all of us.

You Could Be an Explorer

Maybe one day you will pilot a submersible, drive an underwater robot, or discover a creature no human has ever seen. The deep sea is still full of secrets, waiting for the next explorer.

Keep exploring our amazing world! Look up instead of down with Understanding Our Universe, or watch life begin in The Tiny Seed.