1) The Great Barrier Reef in Australia is the largest living structure on Earth and can be seen from space.

2) The President of the United States serves as the head of state and the head of government, responsible for leading the executive branch and representing the nation domestically and internationally.

3) The Earth's core is primarily composed of iron and nickel and is as hot as the surface of the sun.

4) In Norse mythology, the Valkyries are divine maidens who serve Odin, the chief god. They are responsible for selecting warriors worthy of entering Valhalla and escorting them to the afterlife. They are often depicted as powerful and beautiful figures, riding winged horses and wielding spears.