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GELFAND’S WORLD - Take a round ball of iron and squeeze it until it is almost twice as dense and fills half its original volume. That's a lot of pressure. Now imagine that this same ball of iron is so hot that it would be a liquid if it were not under such pressure. But under enough pressure, it has become a solid.
This is a somewhat simplified image of the earth's central core, as explained in a recent talk by USC seismologist John Vidale. The details of how this solid iron core rotates -- and every once in a while reverses direction or at least does something different -- has been of interest to earth scientists. As Vidale explains, there is not complete consensus, but there is considerable data to suggest that the core shows changes in its form and movement over multi-year intervals.
Now shift your mental image to one of those scenes of steelworkers pouring out giant ladles full of molten iron. The liquid iron in those ladles is one way to think of the fluid which surrounds that solid iron core. The central iron core basically sits in a bath of the same element and together, that solid iron core and the surrounding liquid iron make up a substantial part of our planet.
There are additional details that are slowly being discovered. For example, the solid core may be a little less solid at the intersection with the molten iron surrounding it. As the core is pushed and pulled by the surrounding liquid, it may deform (just a bit) from its spherical form.
I bring up these points partly because they are interesting in themselves, but also because they illustrate some important elements of how science is done and how scientific ideas evolve.
Let's start by pointing out the obvious: We cannot look at the earth's core directly. It is a long way down, under a couple of thousand miles of rock and very hot liquid iron. You couldn't drill a hole that deep, and even if you could, you can't scuba dive through molten iron.
So everything we learn about the center of the earth has to come from indirect evidence. It is a difficult idea for some people to wrap their minds around. But there it is -- we can learn new things based on the already known laws of physics and chemistry as applied to new information obtained from seismometry data.
And what is that, you ask? It is the record over time of how intensely the earth under our feet shakes. You've all seen it on the television news when we have an earthquake. We see the needle jump up and down, creating a graph that looks like some bizarre sculpture.
The seismologists have learned to read those squiggles so as to obtain useful information. We are used to hearing from the US Geological Survey about the location of an earthquake, its intensity, and how deep under the ground it occurred, all based on analysis of those waves as they hit detectors in different places. This is an example of using an indirect source (how hard the ground is shaking right here) to figure something out about an event that happened in a place that we can't even see (because it is miles underground).
So now let me tell you about an observation that allowed Vidale and others to figure out something about the core. A number of years ago, there was an earthquake that originated way down in the southern hemisphere. Three years after that quake, there was another quake that was pretty close to where the first earthquake occurred. Now imagine a seismometer located on the opposite side of the earth -- in this case in the northern hemisphere.
The scientists could distinguish between earthquake waves that traveled down into the earth and through the core vs. waves that traveled near the core but not actually through it. And looking at records of such seismometry data taken from events that were years apart, there were differences in the time it took for the waves with the longer path to reach the instrument. When you look at the data, there is a slight change in the time of arrival in the northern hemisphere. And this result can be used to infer something interesting about the earth's core.
Now this may sound complicated and indirect. It is.
Not only that, but it was the culmination of a series of conclusions, inferences, and experimental testing that went back many decades. In short, the science of seismometry is based on the physics of waves (but flowing through rocks instead of water) and the theoretical inferences that one can draw based on taking informed guesses about how the earth is structured.
Out of this has come a model for how the earth looks if you imagine it through and through.
And one more element of this story. It turns out that there are lots of things that remain unknown about the earth's structure, and there are controversies about everything including how fast the core rotates and whether or not it reverses direction every now and then. Some folks will find the lack of absolute knowledge frustrating, but it is the motivating force for the scientists who ask questions and think they can find answers.
The astute reader may notice a certain similarity between this story and the book Freakonomics, in the sense that the scientists (or in the case of the book, University of Chicago economists) are taking advantage of events that they did not plan in order to consider the validity of some hypothesis they would like to test. The economists took advantage of getting hold of a drug dealer's financial records and used them to develop a picture of the economic foundations of drug dealing in Chicago. Our local scientists cannot order the earth to shake, but they can take advantage of earthquakes that happen by themselves.
I raise these issues to illustrate the fact that science is often difficult, and it takes time and work to figure things out. There is the additional (but important) point that it takes skill and intelligence to sort through the data (those squiggles on the seismograph) in order to figure things out.
And this all leads to my editorial remark.
There was an analogous process in the development of organic chemistry -- we can't see molecules with our eyes, but we can figure things out by following the results of chemical reactions and making observations of things like the absorption of infrared light by the atmosphere. The result from doing the latter measurements is the understanding that atmospheric CO2 levels have been going up for many years. There is an additional conclusion -- based on the idea that absorption of energetic light on a huge scale can warm the surface of the earth, the air, and (importantly) the oceans -- and thus came the prediction of global warming.
And out of this prediction came the corollary, that our climate would inevitably change as a result.
Like I said, getting to such theoretical conclusions, now demonstrated by the increasing ferocity of hurricanes, our recent fires, and earlier onset of Spring, is hard work which requires knowledge and intelligence. When some ignorant person refers to these conclusions as a "hoax," the rest of us should understand that this statement is not based on scientific rationality, but a low level of self-serving illogic.
At the same time, we have to admit that every once in a while, one of those scientific conclusions that is merely tentative will fall out of favor as new information comes in and as new experiments are completed. Those who maliciously attack science itself on the basis of evolving theories are wrong in thought and in ethics -- the ability of science to develop new ideas and to hone existing theory based on new information is its essential strength, and should be honored.
(Bob Gelfand writes on science, culture, and politics for CityWatch. He can be reached at [email protected])
