There are islands everywhere — tiny dots in the ocean, big chunks of jungle, rocky bumps in a lake. They look like someone dropped land into the water and walked away. But nobody dropped them. Islands build themselves, and they have three very different ways of doing it.

The loudest way is volcanoes. Deep under the ocean, the Earth's crust has cracks, and hot melted rock called magma pushes up through them like toothpaste squeezed from a tube. It piles up on the seafloor, layer after layer, year after year, until the pile breaks the surface and becomes an island. Hawaii is a volcano island. It's still growing.

The slowest way is coral. Coral looks like colorful rock, but it's actually millions of tiny animals living together in one big apartment building made of their own skeletons. When they die, their skeletons stay put. New coral grows on top. Over thousands of years, the pile gets so tall it reaches the surface — an island made of bones.

The sneakiest way is breaking off. Long ago, all the land on Earth was connected or close together. Then the continents drifted apart like puzzle pieces sliding across a table. Some chunks got left behind in the ocean. Other islands broke off more recently when rivers carved through land, or when the sea level rose and flooded a valley, leaving hilltops sticking out as islands.

Once an island exists, it doesn't just sit there. Seeds blow in on the wind. Birds land and poop out more seeds. A coconut floats across the ocean and sprouts on the beach. Within a few hundred years, an empty rock island can be covered in trees, full of birds, crabs, and bugs that all arrived by accident.

Some islands are temporary. Volcanic islands can sink back into the ocean when the hot spot underneath moves away and the rock cools and gets heavy. Barrier islands — the long skinny ones near beaches — shift and shrink and grow depending on storms and currents. The ocean is always rearranging its furniture.

And some islands shouldn't exist at all, but do. There's a kind called a pumice raft — a floating island made of volcanic rock so full of air bubbles that it doesn't sink. It drifts across the ocean for months, carrying crabs and barnacles to new homes, until the waves finally break it apart.

So the next time you see an island on a map, remember: it either exploded up from below, got built by tiny animals one skeleton at a time, or broke off from somewhere else and floated away. The ocean is full of land that made itself.