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of Philosophy Science 1 of 4 Stable Isotopes Most elements come in a variety of isotopes. In chemical reactions, different isotopes of an element react similarly but not exactly the same: a lighter isotope is a little more reactive/volatile than a heavier isotope. This leads to isotopic fractionation in the products: the isotopic ratios in the product are not the same as the isotopic ratios in the reactants. The degree of fractionation is very predictable for a given chemical reaction and set of conditions. Water vaporizing and crystallizing example Water is made of 1H, 2H, 16O and 18O (and very minor 3H and 17O). When water evaporates, the lighter isotopes vaporize more readily, so that the vapor is enriched in light isotopes and the residual liquid is enriched in heavy isotopes. Similarly, when ice crystallizes from vapor (cloud formation), heavy isotopes are concentrated in the solid phase and light isotopes are residually concentrated in the vapor phase. By measuring the isotope ratios in rainfall, you can tell how "far" the water is from the sea (its origin). If you know the initial isotope ratios of water flowing into a body of water, you can determine how much evaporation has occurred by measuring the isotope ratios in the water. What controls isotopic fractionation Chemical reaction, including biological influences (For example, corn produces much more strongly fractionated carbon than wheat does.) Temperature (Pressure does not play a large role) What controls isotope ratio Initial ratio in reactants Different sources have different ratios. For example, water from the mantle has different isotopic ratios than seawater. The isotopic ratio of 13C to 12C in the atmosphere has changed over geologic time, due to such influences as removing fractionated carbon into carbonate beds or oil. Original fractionation (reaction including biological mediation, temperature) Post-origin fractionation (reaction including biological mediation, temperature) What can you do with isotopic ratios or Why am I telling you this If you measure isotopic ratios and know enough ancillary information, you might be able determine one of the controls on isotope ratio. For example, we know the isotopic fractionation of evaporating water from the sea including its temperature dependence, we know the isotopic composition of seawater, and by measuring the isotopic ratios in water vapor, we can estimate the temperature at which it evaporated. If we did not know the vapor came from seawater, we would have some combination of temperature and possible isotopic ratios of the source. There are a lot of attempts to use carbon or oxygen isotope ratios as paleo-thermometers: the difficulty lies in having adequate control on initial reservoir ratio, the reaction, and post-deposition reactions to reliably interpret this as temperature. Isotope geology requires painstaking attention to detail and is often thwarted by contamination and poor controls. Greg Pouch 2001-09-25 12:32:00 Philosophy of Science 2 of 4 Science The goal of science is to form explanations of observations, preferably predictive and quantitative. Scientific theories should be testable, objective, and quantitative if possible. They should provide explanation of both occurrence and non-occurrence: they should explain why/how things that happen do happen, and why/how things that don t happen don t happen. The phenomena that science describes should be open to observation and, if possible, experiment. Super-natural explanations specifically and a priori excluded as scientific theories. Science deals mainly with what/how/why, but not Why (i.e., science does answer questions like "Why do animals need air?", "Does the earth have a beginning?" but not "Does the universe have a purpose?" Science is based on the fundamental assumptions that 1) The natural world is worth knowing about; 2) The natural world works in a consistent and predictable way; 3) Observations of phenomena are largely observerindependent (objective reality). Science is the process of forming testable explanations of observations. Science distinguishes itself more in how it discards explanations and what/how it is willing to explain than how it forms explanations. In science, it is very important to distinguish clearly among 1) Assumptions, doctrine, dogma, postulates (Ideas accepted without testing, such as Aristotelian logic) 2) Observations, experiment, empirical knowledge. This includes both what does and does not occur. 3) Conjecture, conclusions, hypothesis, theory, model Theory (a framework of principles) is used in the sense of hypothesis (unproven explanation of accepted observations). Model is also used in the sense of explanation, but is generally applied to a particular situation. A model or theory is good or bad based on whether it explains a set of observations and fits with other assumptions. A theory/model can never be proven to be true, only to be not-yet-known-to-be-false. In order to be "true" or true enough, it must be possible for the explanation to be shown to be false. Examples: uniformitarianism is not a theory, because you could not show it to be false; plate tectonics is a theory because you could show that locations don't move relative to each other, or that locations on a single plate move relative to each other; plate motion has become an observation due high to precision surveying. In other realms, theory is used to denote a set of basic assumptions (doctrine, dogma) used in explanations [this definition is common in law], or to denote derisively that something is not an observation. In geology, Uniformitarianism (the present is the key to the past) is doctrine/dogma. That partial melting of basaltic rock produces andesitic rock is an empirical result, and the claim that the rocks in the Andes mountains have largely resulted from partial melting of subducted oceanic crust is a theory (or composite thereof). A given set of claims may be taken as fact in one situation when it is considered in another. Most scientists do not worry very much about philosophy of science issues. Science is not without doctrine, and in fact is very rich in doctrine. People do not just go out and gather a lot of observations then try to explain them: generally, you have a very good idea what might be found. In science, who made an observation or invented a theory should be irrelevant: it should be judged on its ability to explain observable phenomena, not the prestige of its author. There is no grand board that decides whether something is designated hypothesis or theory. There is not some magical "scientific method" that is guaranteed to work. There are a number of different scientific techniques, none of which are guaranteed. Usually, a theory replaces another theory if it can explain the realm of the previous theory, plus some new realm or is "smoother" or explains things better. Often, a theory is used even though known to be not true because it is easy to work with and is close enough. Most surveying is done on the assumption of a flat earth. Greg Pouch 2001-09-25 12:32:00 Philosophy of Science Finish and publish/apply Good Quit and find a new project 3 of 4 Yes No No New hypothesis Hypothesize Test ? No New observations Observe Bad Claim success and hope no one notices Claim success and ridicule doubters (The Emperor's New Clothes approach) Alter data (rare) or discard data (not rare enough) or mis-interpret data (common) Invent ridiculous explanation for bad (measurements or bad original theory. Question underlying assumptions Define Problem Scientific Revolution Assumptions What is accepted as fact? What is important? What counts as an observation? None of the algorithmic theories of science explain the actual process well, and attempting to follow them generally wastes much time. Current Theories of Science Popper falsifiability and verisimilitude (approach to truth). Science progresses by making clearly falsifiable assertions (hypotheses) and hypothesis testing. Kuhn normal science and scientific revolutions. Theory as Paradigm. Paradigm is theoretical perspective from which subject is viewed (e.g. pre-plate tectonics theories, which tended towards the very arm waving elevator tectonics). Normal science is gathering observation on particular situations and using the paradigm to explain them. Contradictions may occur between the paradigm and observation, and are explained within the theory or by minor adjustments or additions. (e.g. hot spots added onto plate tectonics) or pointedly ignored. When enough contradictions accumulate, the science enters a period of un-ease and other theories may gain adherents. (e.g., elevator tectonics for Archean). Eventually (hopefully), a better theory is developed and accepted. Greg Pouch 2001-09-25 12:32:00 Philosophy of Science 4 of 4 Recognizing good science Put up or shut up! William Shakespeare, King Henry IV, Part I, Act III, scene I Glendale I can call up spirits from the vasty deep. Henry Percy Hotsdale Why, so can I, or so can any man, But do they come when you do call them? Glendale And I can teach thee, cousin, to command The devil. Henry Percy Hotsdale And I can teach thee, coz, to shame the devil By telling the truth; tell the truth and shame the devil! If thou have power to raise him, bring him hither, And I ll be sworn I have power to shame him hence. O, while you live, tell truth, and shame the devil! Mt 7, 15-20 (NAB) Gospel reading for June 28, 2000 Twelfth Wednesday in Ordinary Time Jesus said to his disciples: "Be on your guard against false prophets, who come to you in sheep's clothing but underneath are wolves on the prowl. You will know them by their deeds. Do you ever pick grapes from thornbushes, or figs from prickly plants? Never! Any sound tree bears good fruit, while a decayed tree bears bad fruit. A sound tree cannot bear bad fruit any more than a decayed tree can bear good fruit. Every tree that does not bear good fruit is cut down and thrown into the fire. You can tell a tree by its fruit." Doctrine in geology Dogmas (Postulates accepted without question) Uniformitarianism (Present is key to past) Acceptance of physics, chemistry, biology Old earth What is important Distribution of rocks and sediments and fractures in rocks Identity, composition (chemical and isotopic), and arrangement of minerals within a rock Origin of rocks and their distribution Depositional and intrusive sequences and gaps therein, along with ages What is accepted as fact? Chemistry, Physics, Meteorology, Biology (sort of) What counts as observation Field studies, chemical analyses, geophysical measurements, airphotos, topography, well logs, specimens Greg Pouch 2001-09-25 12:32:00

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