The earth may be extremely old.
Humanity may be not.
As far as far as the techniques and evidence, I want to laugh a bit, so I think Always Sunny explains the situation well.
https://www.youtube.com/watch?v=Zgk8UdV7GQ0
What it boils down to is that 99% of us don't actually "know" things. We're "told" things and then we accept them. What we actually know is very limited to our first-hand experience.
Almost none of us has researched it ourselves. Almost none of us have looked at the data. Almost none of us have actually participated in these studies and tests.
That includes all of their evidence, all of the supposed techniques they use. We really take their claims for granted that they actually work, but the problem is that there are so many gatekeepers when it comes to these things that control the flow of knowledge that even a corrupt individual present at one point in the process can severely hinder or outright stop the truth from coming out.
I'm not saying that everything is a lie, but I think we really need to consider how much we KNOW and how much we were TOLD.