The tallest unclimbed mountain in the world is Gangkhar Puensum in Bhutan, off-limits due to local spiritual beliefs.

The longest cave system in the world is Mammoth Cave in Kentucky.

There have been five mass extinction events in Earth's history — and we may be in the sixth.

The Sahara Desert is roughly the size of the United States.

Antarctica is technically a desert — it receives less precipitation than the Sahara in many areas.

Mount Everest is not the closest point to space — that distinction belongs to Mount Chimborazo in Ecuador, due to Earth's equatorial bulge.

Lake Baikal is the deepest freshwater lake in the world.

The Nile River delta is fertile farmland.

The Ice Age shaped many of today’s landscapes.