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

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

3) Political campaigns involve strategic activities, such as advertising, public appearances, and grassroots organizing, aimed at promoting a candidate or political party and gaining support during elections.

4) Robert Downey Jr. is an American actor known for his portrayal of Iron Man in the Marvel Cinematic Universe. He has also starred in films such as "Sherlock Holmes," "Chaplin," and "Tropic Thunder," and has received critical acclaim and commercial success for his performances.