Earth is a Grimoire card from the original Destiny (Destiny 1), found under Places → Earth. Grimoire cards held most of the game's lore and were read on Bungie.net and in the companion app, not in the game itself.
Card text
Once our cities lit the whole world. Now we huddle under the shadow of the Traveler, in the last place it protects. It is so very fragile, this small blue ship, our home.
Grimoire text written by Bungie, shown as it appears in the Destiny 1 game files.