Figuring out the past (in part to try to understand the future) via the scientific method (such as
limnology and
dendrochronology) produces lots and lots of small facts.
People use these small facts to build up an hypothesis, then get it out there for peer review.
The ideas that hold up, are used to describe how things work according to our best current knowledge.
When new ideas come along, if they better describe what is going on or predict things better, old ideas are let go.
Right now, our man-made historical records are not all that great in terms of geological time, but the earth time records through study of lakes, rivers, earth, stone, sedimentation, etc, are very good, just not on human time scale (though the two I pointed out above are actually pretty good human time adjuncts).
As time goes along, us humans are getting better with what has happened in the past and when. Maybe we are still in the stone tools and bearskins stage (what they will say 500 years from now), but we got the tools to do some rudimentary discovery, recording, and projecting, so why not make some conservative proclamations and see if we can learn from ourselves while not making things worse?