Geology For Dummies. Alecia M. Spooner

Чтение книги онлайн.

СКАЧАТЬ tested through multiple experiments and is accepted as true by the scientific community. But the work doesn’t end there! Scientists will continue to test hypotheses about the details within a theory, filling in gaps in understanding and looking out for incorrect assumptions that can be corrected to strengthen the theory.

      Scientific theory versus scientific law

      Scientific theories are not waiting to blossom someday into scientific laws. Laws and theories in science are two very different things.

       A scientific law describes an observed action that, when repeated many times, is always the same. For example the law of gravity states that two objects will move toward one another. This movement is observed every time you drop something. The object you drop is attracted to the earth. The law of gravity simply describes this action, which is demonstrated to be the same in every test.

       A scientific theory explains how a set of observations are related. For example, the theory of gravity seeks to explain how the relationship of two objects (their relative size, weight, and distance from each other) results in the observed interaction described by the law of gravity.Both a scientific law and a scientific theory could be accurately described as “fact.” Both are developed out of hypotheses that have been tested and proved true. A well-tested and generally accepted theory is considered true even though it may still be tested by the proposal of new hypotheses and experimentation. In some cases, part of a theory may be shown to be untrue, in which case the theory will be adjusted to accommodate this new truth without the entire theory being called into question.

      The road to paradigms

      A really thorough, well-tested, and widely accepted theory may become the current scientific paradigm. Scientific paradigms are patterns that serve as models for further research. Right now, plate tectonics theory is the paradigm within which all new geologic research takes place. The explanation provided by plate tectonics theory is accepted as proven true, and most researchers seek to answer questions that refine their understanding of this process rather than seeking to disprove the theory as a whole.

      Paradigms, like theories, may change with new information; the change is called a paradigm shift. A paradigm shift brings a new perspective — a whole new way of looking at things. For example, the acceptance of the ancient age of the earth was a paradigm shift for early geologists. These scientists had struggled to explain how geologic features were created in the short span of a few thousand years (previously accepted as the age of the earth). The new paradigm of Earth being billions of years old provided a framework within which geologic processes had plenty of time to occur, creating the features they observed. (See Chapter 3 for more discussion about this particular paradigm shift.)

Speaking in Tongues: Why Geologists Seem to Speak a Separate Language

      As with many sciences, when you begin to study geology you may find yourself overwhelmed by all the new words that you have to learn. Indeed, geologists have their own language for describing rocks, earth processes, and geologic features. But after you get the hang of what all the different words indicate, reading about geology is much less intimidating.

      Lamination vs. foliation: Similar outcomes from different processes

      Geologists describe characteristics of rocks with the intention of understanding the processes that formed those characteristics. For this reason, an observed characteristic, such as “layers,” will have different terms indicating what kind of process resulted in those layers. Here’s an example of what I mean:

       A rock with layers may be described as laminated. Laminations are thin layers formed by the accumulation of tiny particles that settle through standing water (such as at the bottom of a lake or pond). This layered (laminated) rock is a sedimentary rock.

       A rock with layers may also be described as foliated. Foliations are thin layers or sheets of minerals that are created by intense amounts of pressure and heat deep within the earth’s crust. This layered (foliated) rock is a metamorphic rock.

      

The layered characteristic of these rocks may seem similar at first glance but is actually the result of very different processes that occur under very different conditions on the earth. Closer inspection of the rocks (perhaps with a microscope) will reveal that the layers made of particles are different in appearance than the layers made of mineral sheets.

      Gabbro vs. basalt: Different outcomes from similar processes

      Another defining characteristic of rocks is their composition, or what minerals they are made of. However, rocks with the same mineral composition may have different names. Why? Geologists want to categorize rocks according to both composition and formation process. An example is the distinction between the rocks called gabbro and basalt.

      Both gabbro and basalt are dark-colored rocks with the same mineral composition. They both are formed by the cooling of liquid rock (magma or lava) into a solid. Gabbro is formed when the liquid rock cools underground, slowly, over a long period of time. Basalt is formed when liquid rock cools very quickly, at or near the surface of the earth where it is exposed to air or water.

The different formation processes create observable differences in the rocks — gabbro has large, visible mineral crystals, while basalt does not — but the composition of the rocks is still the same. By giving them different names, geologists can categorize a rock with a term that includes information about both composition and formation characteristics.

      

When studying geology it is very helpful to have a dictionary of geologic terms or dictionary of earth science handy to help tackle the immense amount of new vocabulary that you will encounter!

Chapter 3

      From Here to Eternity: The Past, Present, and Future of Geologic Thought

      IN THIS CHAPTER

      

Using catastrophe to explain geologic phenomena

      

Proposing origins for Earth’s rocks

      

Arriving at modern ideas about the earth

      

Using today’s processes to understand the past

      

Unifying theories with plate tectonics

      

Continuing to ask questions

СКАЧАТЬ