How Many Continents Are There?

Part One · The gold star

Arlo held his geography quiz up to the screen so his cousin Lucia could see the gold star. The first question was, "How many continents are there?" Arlo had written seven. Lucia, who lives in Chile, squinted at the paper over the video call. "That is wrong," she said. "There are six. My teacher told us so." Arlo looked at his star. It suddenly felt a little less shiny. One of them had to be wrong. Didn't they?

First they needed to agree on what a continent even is. Arlo read it out loud. A continent is a very large piece of land. In the neat version of the idea, water separates it from the others. But there is no strict rule for how large, or how separate. Continents are counted by custom, by what people have agreed on. Different places agreed on different answers. So the count runs from seven all the way down to four.

Part Two · Six, five, four

Lucia pulled up a map and put her finger on Panama. There, North America and South America are joined by a thin strip of land. At its narrowest point, it is only about thirty-one miles across. "See?" said Lucia. "They touch. So it is one continent, America." Many schools in Latin America teach it that way, and so do schools in Greece. Her six were Africa, America, Antarctica, Asia, Europe and Oceania, which is Australia and the islands around it.

Arlo was not ready to give up his star. He looked up how American schools came to count seven, and found a surprise. Old American atlases did not always split the Americas in two. Some of them still showed one big America until the 1940s. Only in the 1950s did most geographers in the United States settle on two. "So my seven only became official when Grandpa was little," Arlo said. Lucia laughed so hard she dropped her pencil.

Then Lucia found a problem with her own answer. If continents must be separated by water, Europe and Asia are in trouble. They are one enormous piece of land, called Eurasia. The line between them is imaginary. It runs south from the Ural Mountains in Russia down to the Caspian and Black Seas. People drew it because they saw the cultures on each side as different. In Russia and parts of Eastern Europe, many people count Eurasia as one continent.

"So there is another six," said Arlo, "just a different six." Then he spotted the five rings on Lucia's water bottle. The rings on the Olympic flag stand for five continents: Africa, America, Asia, Europe and Oceania. Antarctica is left out because nobody lives there all year round. The people at its research stations are visitors, mostly scientists, along with the pilots and cooks who help them. Five rings, and still nobody was wrong.

Lucia wanted to see how small the number could get. Africa touches Asia too, at a narrow strip of land in Egypt. So try counting every piece of land that is joined together as one. You get four. Africa, Europe and Asia join up as one, called Afro-Eurasia. Then come America, Antarctica and Australia. "Four," said Lucia. "My teacher is going to love this." Arlo was less sure that his teacher would.

Part Three · Under the sea

Then they found geologists, who ask a different question. They care about the rock underneath. The crust under a continent is thicker than the crust under the deep ocean, and lighter for its size. So it rides higher, the way a thick block of wood sticks up farther out of the bath than a thin one. In 2017, a team of geologists used that rule to argue for a continent hiding near New Zealand. They called it Zealandia, a name another geologist had first suggested years before. Lucia had never heard of it, and neither had Arlo.

The strange part is that almost all of Zealandia is underwater. New Zealand and the island of New Caledonia are just its highest bits, poking out of the sea like the tips of a sunken table. Its crust is thinner than most continents have, but everywhere thicker than the ocean floor around it. Some geologists are not convinced it counts. "So there might be eight," Lucia whispered, as if it were a secret.

Part Four · Moving pieces

There was one more twist. The continents are moving right now, about as fast as your fingernails grow. Long ago, almost all the land was joined in one giant continent called Pangaea. The name comes from Greek words for "all" and "Earth." It began to break apart roughly two hundred million years ago. In 1912, a German scientist named Alfred Wegener made a bold claim. The continents, he said, had once been joined and had slowly drifted apart. One of his clues was that the coasts of Africa and South America fit together like puzzle pieces.

Wegener also pointed to the same kinds of fossils on both sides of the Atlantic Ocean. Today, the pieces are still on the move. Africa is slowly splitting in two along a long crack called the Great Rift Valley. Someday, far in the future, the continents may crowd together into another supercontinent. Arlo stared at the globe on his desk. "So one day," he said, "the right answer might be one again."

The next morning, Arlo added a note under his gold star. Seven, the way his school counts. Six, the way Lucia's does. Another six in Russia. Five on the Olympic flag. Four if all the joined land counts as one. Maybe eight under the sea. Once upon a time, one. He was not wrong, and neither was Lucia. Try it yourself: ask someone who went to school in another country how many continents they learned.