Indeed at best there will be scientific evidence to support belief, but proof in God only comes by faith that leads to a deep personal relationship with Him.
As I understand it, the Hebrew word for “day” used in Genesis is YOM. This can have a meaning other than one 24 hour day, as in “an unspecified period of time.” (We can use the English word day that way as "In George Washington’s day the people . . . .) Of course an Internet search will find sources claiming that in Genesis the day really meant a literal 24 hour period and other sources that feel the Genesis day could have a more flexible meaning.