Dirt

Dirt is a type of block that was introduced very early in the game. It uses the same texture on all six sides of the block. Dirt is abundant on normally generated maps, making up the three to four layers between  Grass and Stone.

When a Dirt block is adjacent to grass and exposed to sunlight, the top layer will eventually be  covered with grass; the exact time this happens is random.

Creative Mode
Dirt has been a usable block in Creative mode since its addition to the  game. Early in Minecraft when there were not many block types, dirt was often used as a building material. Since then, more suitable blocks for making structures have been added, and dirt is now used mainly for  altering the terrain of a map.

Alpha Mode
Dirt is easy to mine and is often acquired in large amounts. It will always drop a resource block, regardless of how it was mined. It can be mined by hand fairly quickly, but using  a shovel will significantly speed up the process.

It is not wise to build permanently with it, as it is a very weak block  and will be destroyed in explosions. Some players keep their Dirt blocks to use as footholds or scaffolding, while others consider it to be  useless.

Dirt currently has no uses in crafting, but using a hoe on it will prepare the block for use in farming.

Outdated Modes

 * Survival Test - Dirt behaves like it does in Creative mode.  Sheep eating grass causes it to turn back into dirt. Dirt  is destroyed in explosions.
 * Indev - Same as Alpha.
 * Infdev - Same as Alpha.

Trivia

 * Dirt is the second most common resource on a natural map, next to Stone.