By far the most common block in the game, earth is everywhere and within a few hours of play, and for the rest of your Deepworld life, you're likely to have more of it than any other game item.
In all biomes there are layers of earth that become progressively harder to mine as you go deeper. Earth looks different depending on what biome you're in. In temperate worlds, for example, earth is brown, while in hell worlds, it's a dark grey. However it is all the same stuff.
How to Obtain
There is no game item easier to acquire than earth. The top layer of earth in all biomes except the deep biome can be mined with any pickaxe and any mining skill level. As you dig deeper, the earth becomes harder, and higher mining levels are necessary to mine it. To mine all the way to the bottom of any world but the deep biome, you need level 4 mining. In the deep biome, you need level 8 mining to reach the bottom of the map. In protected worlds, or inside of protector radii (including dungeon protectors), you can use a shovel to temporarily displace earth in order to navigate.
Once upon a time, it used to be possible to place earth in the sky without having it automatically disintegrate.