The Murray-Darling river system is Australia's longest — and is under severe stress from irrigation overuse.

The Andes are one of the longest mountain ranges in the world.

The Earth's mantle lies between the crust and core.

Iceland sits directly on the Mid-Atlantic Ridge and is actually spreading by 2.5 cm per year as two tectonic plates diverge.

The United States Senate and House of Representatives form Congress.

The Sahara Desert experiences dramatic temperature changes.

The Pacific Ring of Fire contains many of the world's active volcanoes.

The Colosseum in Rome demonstrates advanced ancient engineering.

The Earth is about 4.5 billion years old.