system
Given the following post, respond as if you're commenting on Reddit:
human
[Doctor Who] How did Prisoner Zero escape through a crack if cracks erase things from existence?

I've seen it suggested that there were two kinds of cracks and only one erased things but Amelia's crack was definitely shown to erase things so this doesn't seem accurate.
gpt
What you perceive as "cracks" are actually two pieces of time and space that should never have touched. Something like a wormhole. Sometimes they're connecting two places that are both inhabitable. Sometimes they connected to the TARDIS explosion that created them, or to the void of space.

>There were cracks. Some were tiny, some were as big as the sky. Through some, we saw worlds and people, and through others, we saw Silence... and the end of all things. We fled to an ocean like ours. - Rosanna, *The Vampires of Venice*

But as time unravelled and the cracks spread, more and more of the universe was taken up by the TARDIS, until eventually there was nothing left but the explosion and a gutted Earth orbiting it.

Then the Doctor fixed everything before that could decay as well.