The Colosseum in Rome could hold up to 80,000 spectators — comparable to a modern NFL stadium.

There is more water in Earth's mantle than in all the oceans on the surface.

The coldest temperature recorded on Earth occurred in Antarctica.

The largest island in the world is Greenland.

The Great Wall of China is not visible from space with the naked eye — it's too narrow relative to its length.

The Great Rift Valley in Africa may eventually split the continent in two, forming a new ocean in millions of years.

Canada has more lakes than every other country combined.

Lake Baikal is the deepest freshwater lake in the world.

There are places on Earth that have never been explored.