Basic Principles:

John Wilkins over at Evolving Thoughts has an interesting post on basic concepts in science; Chris Rowan at Highly Allochthonous has posted several times on similar topics. I thought maybe I would dip my fingers in this topic too, to whit:
There are certain things you have to take for granted (not on faith, the evidence is there) when doing geology, whether it is in the field, or in the lab, or even in the classroom. Regardless of what young earthers, ID proponents, or just your garden variety of creationist say, there is no need to reinvent the wheel:

1. The earth is very, very old. 4.6 billion years old in fact. There is literally tons of evidence of this, thermodynamic, radiometric, and other models all state the earth is old, some with more accuracy than others. The oldest rocks on earth are reliably dated to over 3 billion years old (Jack Hills metaconglomerates show 4.4Ga), why there aren’t older ones is covered in 2. The concept of a very old earth is just as basic in geology as a very old universe is basic in astronomy and cosmology. These tend to reinforce one another, and I have not seen anyplace that they contradict. The Old Earth is axiomic.
2. The surface of the earth is a dynamic place, even though the time scale is very slow compared to our observations, the evidence of changes, both catastrophic and gradual changes in the rock formations, surface deformation, continental position and most important to life, the environment, are preserved in the rock record. This record has to be interpreted. That interpretation is really what geology research is all about. That the earth has changed over time is also axiomic, how and why can be debated, but that the earth did is not.
3. Life evolved. How, life started is an open topic for now, at what threshold you call something living? That debate will go on for some time. Life did start at some level (very simple living things) long ago. There are fossil stromatolites that date comparably to some of the oldest rocks known, 3.465 Ga from the Apex Chert microfossils from Australia. Life may have spent several billion years hanging around as simple cyanobacteria, but it did change, as its environment changed. These changes grew and added to the diversity of life, eventually leading to entirely new organisms, including us. That this change, this evolution occurred is also an axiom.

Using this knowledge of the past, and these basic principles, predictions can be made about what should be found, and even where. This has led to new discoveries of fossils and formations that continue to intrigue and occupy scientist and geologist.