Figure 1. Scientific Method Flow Chart.
What's the "Science" in Earth Science?
The sciences are a group of disciplines that have a common approach to finding out how aspects of the universe work. This approach, called the "scientific method", is designed to be unprejudiced: one does not have to simply believe a particular researcher. Scientific findings are not accepted based on the prestige or convincing powers of the proponent, but on the results obtained through observations and/or experiments which can be (and are) reproduced.
The Scientific Method (Fig. 1) is a series of steps, designed to meet these objectives:
1. OBSERVE. Make observations on some aspect of the universe.
2. HYPOTHESIZE. Make an "educated guess" to explain the observations.
3. PREDICT. Use the hypothesis to predict other aspects of the nature of the universe.
4. TEST. Test the predictions by experiments and/or further observations.
5. MODIFY. If the predictions are not supported, use the experimental results and/or new observations to modify the hypothesis and then repeat steps 3 and 4.
6. THEORIZE. When all the predictions are supported by the experiments and/or new observations the hypothesis becomes a theory. A theory is a conceptual framework that explains existing observations and predicts new ones.
Figure 1. Scientific Method Flow Chart.
In some scientific disciplines it is difficult to conduct experiments (earth science is one, astronomy is another). Hypotheses in these disciplines can be tested by the collection of further observations and measurements. For example, if you hypothesize that a large volcanic eruption will change some aspect of climate patterns, you can’t create a large eruption to find out if you're right. Instead you could wait for an eruption to occur and then observe the climate changes or you could collect observational evidence that had been recorded for eruptions in the past.
An important characteristic of a scientific theory is that it must be "falsifiable". This means that there must be some experiment or possible observation that could invalidate the theory. For example, the theory that all earthquakes are caused by invisible aliens that we can not detect is NOT scientific - by definition there is no way to disprove this theory, so it is not falsifiable.
Is a scientific theory "the truth"? When a theory is said to be "true" it means that it agrees with all known experimental and/or observational evidence. When a theory cannot explain new observations it will have to be replaced by a new theory. This does not mean that the old theory was "wrong" or a "mistake", only that the old theory had limited applicability and could not explain new observations. The only "true" thing about currently accepted theories is that they explain all currently available observations, which, of course, does not imply that they will explain all future observations! No matter how good a theory is, it can not be "absolute truth" (i.e. no possibility of change).
Competing Explanations in Current Scientific Theories.
One of the consequences of the scientific method is that well-established and widely-accepted theories can still contain elements that are not fully understood and are explained by several competing hypotheses. A good example is the theory of plate tectonics which has revolutionized modern geology. A vast amount of scientific evidence supports the central theme of the theory that the earth's outer rock layer (lithosphere) is fractured into large pieces (plates) which move around the globe, carrying overlying oceans and continents with them. The theory has correctly predicted the distribution of earthquakes, volcanoes and mountain chains, greatly improving our understanding of geology. However, not all aspects of the theory are fully explained - the driving force behind plate motion is the subject of several competing hypotheses:
1. The Convection Cell Model: large convection cells in the earth's partially molten mantle exert a drag on the overlying plates, carrying them along like objects on a giant conveyor belt (Fig. 2).
Figure 2. The Convection Cell Model.
2. The Push-Pull Model: the creation of new oceanic plate at spreading centers pushes the plates away on either side and, at the same time, colder, denser plate material sinks at subduction zones pulling the plates along behind them (Fig. 3).
Figure 3. The Push-Pull Model.
3. The Plume Model: isolated plumes of hot mantle material rise up under a plate, pushing it up and breaking it into three pieces separated by rifts (fractures in the plate). As the plume diverges, it drags the plate fragments away from each other and the rifts widen to become oceans (Fig. 4).
Figure 4. The plume model.
The correct hypothesis (or combination of hypotheses?) is uncertain because it is difficult to test explanations that involve processes occurring hundreds of miles below the earth's surface, operating over millions of years. As our ability to observe, measure or model these processes improves (i.e. due to technological advances) a clearer picture of what drives plate motion should emerge.
The Interdependence of Science and Technology
What's the difference between science and technology? Whereas science is a procedure for acquiring a better understanding of how the universe works, technology provides the tools for testing scientific ideas. Once again, the theory of plate tectonics provides a good example of this relationship between science and technology.
The fundamental core of plate tectonic theory is that plates are created at mid-oceanic ridges (spreading centers), move away from the ridge, carrying oceans and continents with them, and are absorbed back into the earth at subduction zones (see Fig. 3 above). Predictions based on this hypothesis were tested using technological tools. Examples include:
1. If new oceanic crust is created at mid-oceanic ridges and then moves away from the ridge, the age of the ocean floor rock and the age and thickness of ocean floor sediment should all progressively increase with distance from the ridge. The Deep Sea Drilling Project, an international program aimed at testing tectonic theory, used the deep ocean drilling vessels the Glomar Challenger and the Joides Resolution to measure the thickness of ocean floor sediment and to obtain samples of sediment and ocean floor rock for dating by modern radiometric techniques.
Figure 5. The Deep Sea Drilling Vessel Joides
Resolution.
The results confirmed these predictions.
Figure 6. Age of the ocean floor becomes
progressively older with distance from mid-oceanic ridges. The mid-Atlantic
ridge is particularly prominent.
2. Magnetic reversals (periodic flipping of the earth's magnetic poles), known to be recorded in rocks on land, should be recorded by magnetic minerals within ocean floor rock and should create a symmetrical pattern of normal and reversed magnetism across mid-oceanic ridges. Magnetometers (devices for measuring magnetism of the earth's surface) towed by research vessels over mid-oceanic ridges confirm the presence of these magnetic reversal patterns.
Figure 7. Symmetrical bands of normal and
reverse magnetized ocean floor rock surrounding part of the mid-Atlantic ridge.
3. If the plates are moving as plate tectonic theory predicts, very accurate positional measurements on fixed locations, taken over several years, should reveal this movement. Two recently developed positioning technologies confirm these movements. Satellite Laser Ranging employs ground-based stations that bounce laser pulses off satellites in fixed orbital positions. Precise timing of the travel time of these laser pulses allows accurate calculation of the position of these ground stations; monitoring of these positions over several years reveals the relative motion of these sites. Very Long Baseline Interferometry uses large radio telescopes to record signals from very distant quasars, which act as fixed reference points. The difference in the arrival time of the same signal can be used to calculate precise distances between the ground-based telescopes. Monitoring over several years shows that these distances change, confirming that telescopes on different plates are moving relative to each other. These modern techniques have revealed that Hawaii is moving towards Japan at about 8.3 cm per year and that the east coast of the U.S. is moving away from Europe at about 1.7 cm per year as the Atlantic Ocean grows wider.
Figure 8. Radio telescope array at Socorro,
New Mexico.