They attempt to raise a new army on Earth using period technology, but are foiled by again the Doctor.

"Earth doesn't use the Art for anything, especially not for something so trivial."

But this is how the Earth used to be, you see, before the ax unleashed their nanotech plague.

Earth uses that as an excuse to launch an invasion.

It has a small yellow sun very much like the one that Earth used to circle, and broad blue seas.

"Earth would use it to force the rest of the Triple to do what it wants."

Earth was using all of its new-found power.

Apparently Earth is using biological engineering for medical purposes.

Earth used this language first, invented these symbols to encode it.

Mineralogists can help find important minerals in the Earth using what they know and learn.