The Earth is a dynamic planet that has changed contin- uously during its 4.6 billion years of existence. The size, shape, and geographic distribution of the continents and ocean basins have changed through time, as have the atmosphere and biota. Over the past 20 years, bold new theories and discoveries concerning the Earth's origin and how it works have sparked a renewed interest in geology. We have become increasingly aware of how fragile our planet is and, more importantly, how inter- dependent all of its various systems are. We have learned
that we cannot continually pollute our environment and that our natural resources are limited and, in most cases, nonrenewable. Furthermore, we are coming to realize how central geology is to our everyday lives. For these and other reasons, geology is one of the most important college or university courses a student can take. <...>

In the example above, an observation is made and a hypothesis formulated. A hypothesis is an educated guess. Experiments are performed to prove or disprove your hypothesis. This sort of deductive reasoning is the same thought process used by detectives to solve crimes. You may consider the mineral identification experiments as simple, but there is no written rule that experiments must be complicated.
If an experiment is repeated time and time again and the conclusions are exactly the same, then the conclusion is elevated to a theory. Scientists define theory as a proven conclusion, something over which there is very little doubt. Notice that the way scientists use the word theory is much different from our everyday use. In our everyday usage, theory is equivalent to a scientist’s hypothesis—an estimation or guess. Sherlock Holmes’ theory of the murder was Colonel Mustard with the candlestick. This is Holmes’ guess or hypothesis of the crime; now he must gather evidence to prove it. <...>

Nearly everyone, at some time in his or her life, will have stood on a  sea beach and watched how the waves repeatedly disturb and then deposit the sand grains, whilst the wind, blowing freely over the drier parts of the beach, gathers up some of the sand and sweeps it inland to form tall dunes.

This particular case, one from common experience, serves very well to introduce the general topic of this book, namely, the dynamic interactions, in natural surroundings, between detrital particles and moving fluids. These interactions, in which physical processes are of paramount importance, give us the depositional landscapes and seascapes with which we are familiar today and, at various removes in time, many of the sedimentary strata found in the earth's crust <...>

Petrophysics, beginning with Archie’s historical yet evergreen equations, has a key function in all applications of geosciences, petroleum engineering and related technologies. It helps us to understand the processes and controlling properties and creates relationships between parameters we can measure as output of the dramatic progress in exploration techniques and properties we need for reservoir characterization (hydrocarbons, water, minerals, geothermal energy), exploration of natural resources, geotechnical constructions and environmental protection.