If no sentient being, capable of communication, is around to witness a certain event in- or alteration of the space/time-continuum as it is artificially applied, it would be quite difficult to prove that things used to be different. The age-old question of wether a bear shits in the woods if nobody's around to see it seems to apply. This makes the whole debate between creationalists and those who believe in the theory of evolution quite pointless. At least, from my point of view.
Consider for example for a moment that Earth would really have been created a short while ago and according to the story one can read in one of the more popular books of creation: the Bible. The first humans weren't heavily into writing things down themselves, and even if they would have been, God had quite an unstable personality during the early times and humans had more important things on their minds, such as surviving God's unpredictable changes of heart. Not that I can blame Him, for if I were creating something like a sentient species and an entire playground for them to enjoy, I would want my creation to be at least perfect; especially when working on/with conscious individuals mistakes are bound to be made, and optimal conditions can sometimes only be figured out by trial and error. Apart from that the Creator is constantly being affected, influenced and changed by His own Creation during the process, as He is forced to learn and reflect upon own His position in relation to His Work in progress. After all, He wasn't quite used to interaction when He started, for up until then, He'd had nothing to interact WITH. God must have slowly realized along the way that by creating conscious beings out of Nothingness (beings in His own image, mind you!) without being able to ask them beforehand wether they considered it to be acceptable to be called into existence, He could at least try to treat them in a respectfull manner similar to the way He expected them to treat Him.
Apparently, at first the Creator probably didn't spend much time contemplating his Creation; He had banished and cursed His first humans from the Garden of Eden, but after that, apart from some minor incidents and events, He doesn't appear to intervene in the lives of Men that much. He helps with some pregnancies, gives some blessings, but other than that, no references to His actions are made. At least, not in the Bible as we know it. Probably He was engaged in more important matters; possibly He still considered the World and His humans as a mere toy or decoration. And suddenly, after hundreds of years have passed on Earth, and many generations have worked and lived according to the rules He set for them, He begins to regret having created Man. In one of His most extreme outbursts He destroys all of mankind (and just about all other creatures living on the land) by wiping them out with a flood, saving only the one specimen, Noah, from which He derived enjoyment (according to the Bible), and enough pairs of creatures from the animal kingdom for all the different species to survive this event.
Now this is a critical moment. At the moment of the flood, the human race had already existed for quite a long time, so it is not unreasonable to assume that humans had developed a bit of knowledge and understanding about the workings of the world in/on which they lived. They were able to communicate with each other, that's for sure, and maybe they already had some form of written language to pass on information to later generations. The Bible doesn't tell us much about the level of sophistication they had attained by the time of the flood, as only some brief geneological data is included. Now it might be that there's plenty of texts on this subject that are not included in the Bible, but then again, I am only using this story here as an example of a way of thinking.
The only surviving humans, Noah and his wife, were stuck on their ark for quite a long time before the waterlevel began to drop again. They are the only two people who were in a position to pass on information about ANYTHING that happened BEFORE the flood. Possibly they had an accurate recollection of EVERYTHING that happened up until then, though this is highly unlikely, as they hadn't been around long enough to witness all of it personally. Supposing even that Noah DID possess the sum of all human knowledge up until that time (remember, we don't know anything about the psychic abilities or perhaps genetic inheritance of memories of these people), he could not possibly have accurately reproduced all of it in time to pass it on to his children. Even though Noah lived to be quite old, he probably spent most of his time trying to survive the harsh conditions he was suddenly subjected to anyway.
Now, even in the highly improbable case that Noah actually did bring a record of absolutely everything that had happened since Creation had started, Noah has no knowledge of what God was up to during the time he and hise wife spent aboard the Ark; below the surface of the water, all traces of civilisation could have been wiped out during that time, and God might have been incredibly busy terraforming. Whatever happened during this period, the only human being capable of communication could not have possibly known about all that was going on, unless he was all-knowing and all-seeing himself.
Remember, I'm not saying anything about the validity of the Bible here. Nor am I trying to actually 'prove' that either, neither or both the Creationalists and the Evolutionists are right or wrong. What the example I have used CAN show, however, is that just about anything could be true or false, as there is always a way to talk your way around things. With words, even the impossible can be presented as something that can easily be accomplished. This particular example could raise any number of questions, and could answer quite a few as well. Did Noah make everything that happened before the flood up himself? If so, then the Creationalists could kiss their arguments goodbye, as this would invalidate the story on which they base their ideas. Or would it? Just because something was made up, doesn't mean it didn't actually happen, too. In this case one just cannot prove it anymore (as long as we leave thoughts about time-traveling alone for a moment). Or, if Noah thought it all up... and if the world had not existed before he began thinking it all up... and if he thought up a world that had been, according to his fantasy, created long before he was around... then that world WOULD have been created long before he was around, simply because he thought it up that way ;-)
As you can see, one can go on forever, thinking about what could or might have been, and so I'll leave that up to you. However, we must realize that in the end, it's all just stories, and though we can learn a lot from stories for use in our everyday lives, they remain stories. Even if we come up with ways to 'prove' that the stories are, in fact, true. So dream away all you wish, but remember to keep an eye on the here and now as well, for that is one story you are actually part of as it unfolds thoughout all eternity. Enjoy!