But Earth knew nothing of them for two thousand years.

We've got to let Earth know, somehow, that they are coming.

Only once did he find any sign that Earth had ever known civilization.

Like they don't know how to live on planet Earth.

And what Earth would soon know or guess could ultimately weaken us.

And we drink in memory of the greatest people Earth has ever known.

A completely different Earth, and we know so little about it yet.

Something had been lost in the dead reaches of space, and only Earth knew love.

Over one billion people on planet Earth do not know how to read and write.

Old Earth certainly had known exactly what was in its solar system.