Time field

A Time Field was a mysterious crack in the fabric of time and space caused by an unidentified explosion that originated from 26/06/2010.

Origin
The cracks in the universe were said to come about from an explosion. When one appeared in 2020, underneath a small village in Wales, the Doctor was able to put his hand in one a retrieved a piece of shrapnel from the explosion. This piece turned out to be a part of his TARDIS which had been broken off and burned. (DW: Cold Blood)

Types of Crack
There were two types of cracks. One type of crack released energy of "pure time" that could wipe individuals out of time itself and remove events from history, though time-travellers such as the Doctor still had the ability to remember them, as long as the removed event or person did not relate to the person's direct past. (DW: Flesh and Stone, Cold Blood) This type of crack seemingly erased events such as the CyberKing walking over London in the Victorian era and the Dalek invasion of 2009, one of Earth's biggest invasions. The other type of crack acted like a wormhole and could be opened to allow a passage between the places on either side. One device known to be able to open this type of crack was a Sonic Screwdriver. (DW: The Eleventh Hour)

Notable Cracks
In Easter of 1996, a crack in Amy Pond's bedroom connected to an Atraxi prison. (DW: The Eleventh Hour) A crack also appeared on the side of Starship UK in the 33rd century (DW: The Beast Below) and in the Cabinet War Room in 1941. (DW: Victory of the Daleks)

Another crack later opened to an incredibly large size aboard the Byzantium spaceship in the 51st century. It erased Crispin, Marco, Pedro, Phillip and many Weeping Angels from existence and subsequently closed. The Weeping Angels themselves had feared it, and attempted to escape, only to be dropped into it after they absorbed all of the Byzantium's energy, disabling artificial gravity. The Angels combined creating a sufficiently complex space-time event that sealed it for a while. (DW: Flesh and Stone)

The crack was mentioned again in Venice, 1580, when Rosanna Calvierri claimed that she and the other vampires were forced to flee their planet which was being consumed by a crack. She also claimed that they saw two different types of cracks; one through which they saw other worlds and people and the other through which they saw only silence and the end of all things. According to her, the cracks could be tiny, or as big as the sky. Just before the Doctor left, however, silence fell over Venice, which he picked up on. (DW: The Vampires of Venice)

There was a crack beneath the Earth in 2020 that the Doctor, Amy and Rory found while leaving the Silurian base. Attempting to investigate the crack, the Doctor reached inside, searching for “shrapnel” from the original explosion, only to find a piece of the TARDIS door, burned and destroyed. Before leaving, Rory was shot by the Silurian, Restac, and came in contact with the light from the crack before the Doctor and Amy could rescue him. Despite Amy's efforts, the Doctor was forced to leave Rory behind, the crack erasing Rory from existence. Although it is implied that the Doctor may still remember him, Amy has lost all recollection of Rory due to the crack directly affecting her past. (DW: Cold Blood)

Chronological Appearances

 * 1580 - Rosanna Calvierri and her people came to Earth after her planet was consumed by a crack. (DW: The Vampires of Venice)
 * 1941 - A crack appeared on the wall of Winton Churchill's Cabinet War Room when the TARDIS left.(DW: Victory of the Daleks)
 * 1996 - A crack appeared on young Amy Pond's bedroom wall. This was when the Doctor first noticed them appearing. (DW: The Eleventh Hour)
 * 2020 - A crack appeared in the rock of a Silurian base, after Rory Williams was shot it consumed him, so that Amy Pond forgot about him, only the Doctor remembered it. (DW: Cold Blood)
 * 3295 - A crack appeared on the side of the Starship UK, just after the Doctor had left. (DW: The Beast Below)
 * 51st century - Sometime in the 51st century a crack appeared in the temple of the Weeping Angels and then consumed them. (DW: Flesh and Stone)

Function
The Doctor stated that the only way to close the first type of crack is for it to consume a complicated space-time event, an example being either him or the Weeping Angels, needing all of them to be equivalent to himself. River Song volunteered to let herself be consumed, but the Doctor laughed at her idea, and stated that she wasn't even as complicated as one Angel. The Doctor, River, and Amy managed to escape the crack by allowing the Angels to drain the ship's power, causing its artificial gravity to switch off and the Angels to fall into the crack, sealing it. At the end of the episode, he traced the origin of the temporal explosion behind the crack to the day of Amy's wedding: 26th June, 2010. (DW: Flesh and Stone) The Doctor clamied that the cracks were growing wider and bigger since his last encounters with them. It was also possible to put a person's hand inside and retrieve an object from inside the crack, as demonstrated by the Doctor when he retrieved a piece of the TARDIS, speculating that it may be 'shrapnel' from the original explosion. (DW: Cold Blood)

Behind the Scenes

 * The Time Crack was inspired by a crack Steven Moffatt saw in his son's bedroom, which resembled a smiling mouth.
 * Moffat has confirmed that the Crack will appear in most episodes.
 * The Cracks arc is, like the previous series (excluding the Bad Wolf meme), foreshadowed in a previous series, in this case in DW: The Next Doctor (though, perhaps unintentionally).
 * The Time Field has caused much debate amongst fans, with many "supposed Cracks" that are actually just clouds and other items of scenery (an example being while under the Earth in Cold Blood, many small cracks are on the walls or The Vampires of Venice where clouds and lighting give the impression of a crack in the sky).