The problem is that hydrogen does not exist by itself on Earth.

No grenades of such power and type existed on Earth.

They were nothing compared to what must exist on Earth.

But how long would man continue to exist on Earth?

Men and dinosaurs had never existed on Earth at the same time.

What is the biggest animal ever to exist on Earth?

What we have here is a substance that can't exist on Earth, so there's no name for it in our language.

The concept of husband and wife, for instance, existed only on Earth.

This is not a power which we knew to exist on Earth before.

Of all species that have existed on Earth, 99.9 percent are now extinct.