How do we know light traveled at the same speed it does today 40 million years ago? Or that the way we date rocks today has any connection to the way they decayed 110 million years ago? IMO, it's a logical conclusion that scientists have "faith" that the present is the key to the past.
Every time you think this, bear this in mind: for every untested assumption in science, there are about 10,000 graduates desperate to prove themselves to their peers and superiors by tearing apart those assumptions and demonstrating them incorrect. Every graduate in science is desperately looking for something new on which to write his next paper. Guess how many untested assumptions are left lying around, unchallenged?
Science is built, not upon assumptions, but upon the tearing down of assumptions.