What is the evidence for the claim that Young Earth Creationism was the mainstream viewpoint in ancient times?

In [my previous question](https://christianity.stackexchange.com/q/15709/58) , I asked about the origins of the modern Young Earth Creationism movement, especially in America. Originally, the question asked when the YEC belief (mainly with regards to a literal reading of the Genesis account of creation) became widespread, and was subsequently informed that the account of creation in Genesis had been read literally by Christians ever since ancient times. What is the evidence for this claim? I'm specifically looking for **evidence that the early church interpreted Genesis 1 literally in a manner consistent with modern Young Earth Creationism beliefs**. The six-day creation and 6000-year-old age aspects may be treated separately, if and when appropriate.