The beginning of 2 hypothesis
Wellll, I suppose it really begins on whether you believe in the uniformitarianism view, or the catastrophism view. Most scientist start at those 2 hypothesis. Each view or belief has their own set of data to support it. It really comes down to personal belief, and which YOU think has the most concrete evidence.
Catastrophism is the view that most of the earth's geological features are the result of latge-scale catastrophies such as floods, volcanic eruptions, etc.
So this allows for a young world. However, it can also allow for a world which is billions of years old. but....
Uniformitarianism is the view that most of the earth's geological features are the result of slow gradual processes that have been at work for millions or even billions of years.
Thus, uniformitarianism only allows for an "old" world.
As I was saying, scientists start with either one. Then they work, to find more evidence on whichever side they belief is right. Of course, they will find a lot that supports both sides, and a lot which 'disclaims' both sides. So,.... it really is up to you which point you start looking.... :nod: