Earth

From Asimov

Earth is a planet in the Foundation universe upon which humans have lived for longer than anyone remembers. Earth features in one of several Origin Myths found throughout the Empire. Its history, however is shrouded in the mists of time.

In the pre-Empirical era, Earth is described as an overcrowded planet suffering from environmental degradation. These circumstances force the inhabitants to live in vast domed Cities, and submit to compulsory euthanasia at age 60. Nuclear radiation covered most of the planet, turning it into a dead world. Eventually, the Galactic Empire was convinced to deliver new, unpoisoned soil to the planet, but for some reason the project was cancelled.

It was once written that Earth was the planet that developed the positronic brain, the reasoning engine inside the robots that enabled humans to settle the galaxy.

Earth was the third planet from its sun (called Sol) and had one large moon (Luna)