Scientists estimate that more than 2 million species may live in the world’s oceans. Yet only about 250,000 have been discovered so far.

“We’re only really scratching the surface of how much we know about the extraordinary diversity of ocean life,” says Maya de Paz. She’s a member of the Ocean Census team.

In fact, humans have explored only about 5 percent of the ocean. Why? For one, the sea is very deep (see “Layers of the Ocean,” below). In some places, it extends more than 6 miles below the surface. That’s deep enough to fit 24 Empire State Buildings stacked on top of one another!

Also, the deepest parts of the ocean are cold and completely dark. The weight of the water above is crushing. Most divers can descend only a few hundred feet. Beyond that, scientists must travel in special underwater vehicles called submersibles or send robots to explore.

Scientists say that more than 2 million species may live in oceans around the world. But only about 250,000 have been found so far.

“We’re only really scratching the surface of how much we know about the extraordinary diversity of ocean life,” says Maya de Paz. She’s a member of the Ocean Census team.

In fact, humans have explored only about 5 percent of the sea. Why? For one, it is very deep (see “Layers of the Ocean,” below). In some places, it extends more than 6 miles below the surface. That’s deep enough for 24 Empire State Buildings to fit stacked on top of each other!

Also, the deepest parts of the sea are cold. And they’re dark. The weight of the water above is crushing. Most divers can descend only a few hundred feet. Beyond that, scientists must travel in special underwater vehicles. These are called submersibles. Scientists also send robots to explore.

The Ocean Census team has already taken part in more than a dozen research trips. They’ve sent remote-operated vehicles (ROVs) thousands of feet beneath the surface. The ROVs have taken photos and videos. They’ve also scooped up sea creatures for scientists to study.

So far, the team has discovered more than 900 new species! Many were found in the deepest parts of the ocean.

“The deep sea often provides the weirdest and most wonderful creatures,” explains de Paz.

One of her favorites is the “death-ball” sea sponge (see photo, above). The strange creature looks like it’s covered in Ping-Pong balls. Scientists spotted it nearly 12,000 feet deep in the Southern Ocean, near Antarctica.

On the other side of the globe, scientists found a sea snail called a limpet. It was discovered about 10,000 feet deep in the Arctic Ocean, near the North Pole. It can survive in both icy conditions and temperatures around 570 degrees Fahrenheit.

The Ocean Census team has taken more than a dozen research trips. They’ve sent remote-operated vehicles (ROVs) deep underwater. The ROVs have taken photos and videos. They’ve also gathered creatures for scientists to study.

So far, the team has found more than 900 new species! Many were in the deepest parts of the ocean.

“The deep sea often provides the weirdest and most wonderful creatures,” says de Paz.

One of her favorites is the “deathball” sea sponge (see photo, above). It looks like it’s covered in Ping-Pong balls. Scientists saw it about 12,000 feet deep in the Southern Ocean. That’s near Antarctica.

On the other side of the globe, scientists found a limpet. That’s a kind of sea snail. It was found about 10,000 feet deep in the Arctic Ocean. That’s near the North Pole. Limpets can live in icy waters. But they can also live in temperatures around 570 degrees Fahrenheit.