Explain and describe plate tectonics.

Four billion six hundred million years ago the Earth is born from a cloud of dust and fire orbiting the sun. In the beginning there are no seas upon the barren Earth. The sun blisters down as poisonous gases swirl about. Racked with volcanoes, bombarded by asteroids and comets, Earth is incredibly hot with a sea of molten rock covering its surface. The early Earth is a world in slow turmoil for many, many thousands of years. 

Over time the Earth cools and separates into several different layers. The matter with the highest density (mostly iron) sinks to form Earth’s solid inner core. This inner core becomes enveloped by a less dense mixture of nickel and iron - the outer core. Surrounding the inner and outer core is the mantle (itself divided into several distinct layers), and over the mantle is the Earth’s crust, a thin veneer of rocky material that covers the planet like the cracked, twisted, lumpy crust of an apple pie.

Earth's outer shell, the lithosphere, long thought to be a continuous, unbroken, crust is actually a fluid mosaic of many irregular rigid segments, or plates. Comprised primarily of cool, solid rock 4 to 40 miles thick,* these enormous blocks of Earth’s crust vary in size and shape, and have definite borders that cut through continents and oceans alike. *[Oceanic crust is much thinner and more dense than continental, or terrestrial crust]. 
There are nine large plates and a number of smaller plates. While most plates are comprised of both continental and oceanic crust the giant Pacific Plate is almost entirely oceanic, and the tiny Turkish-Aegean Plate is entirely land. Of the nine major plates, six are named for the continents embedded in them: the North American, South American, Eurasian, African, Indo-Australian, and Antarctic. The other three are oceanic plates: the Pacific, Nazca, and Cocos.

The relative small size of the numerous other plates neither diminishes their significance, nor their impact on the surface activity of the planet. The jostling of the tiny Juan de Fuca Plate, for example, sandwiched between the Pacific and North American Plate near the state of Washington, is largely responsible for the frequent tremors and periodic volcanic eruptions in that region of the country.

Powered by forces originating in Earth’s radioactive, solid iron inner core, these tectonic plates move ponderously about at varying speeds and in different directions atop a layer of much hotter, softer, more malleable rock called the athenosphere. Because of the high temperatures and immense pressures found here, the uppermost part of the athenosphere is deformed and flows almost plastically just beneath the Earth’s surface. This characteristic of the athenosphere to flow allows the plates to inch along on their endless journeys around the surface of the earth, moving no faster than human fingernails grow.

One idea that might explain the ability of the athenosphere to flow is the idea of convection currents. When mantle rocks near the radioactive core are heated, they become less dense than the cooler, upper mantle rocks. These warmer rocks rise while the cooler rocks sink, creating slow, vertical currents within the mantle (these convection currents move mantle rocks only a few centimeters a year). This movement of warmer and cooler mantle rocks, in turn, creates pockets of circulation within the mantle called convection cells. The circulation of these convection cells could very well be the driving force behind the movement of tectonic plates over the athenosphere.

Science is Method Based

The Scientific Method is Slow

Conducting a scientific research project is extremely difficult and time consuming.  A properly conducted research study can take from 2 to 5 years to complete.  It is very rare that a researcher can complete a project in less than 2 years. 
 

The steps in conducting a research project include the following:

1. Review the previous literature and find out what other researchers who have looked at this topic have found.  The researcher must read virtually everything that has ever been written on her/his topic befoe she/he can be sure her/his research is properly designed and original.  This process can take years, particularly if the researcher is starting into an unfamiliar research area.
2. Generate hypotheses based on the current theories.  The researcher must evaluate the various theories, find gaps or conflicts in the theories, and then come up with a proposed hypothesis to fill the gap or resolve the conflict
3. Develop a method to test the hypothesis.  If people already knew how to test the hypothesis, or if the methods had already been tried in this area, there would be little need for additional research, so, researchers are frequently having to develop new research methods and techniques, invent new equipment and machinary, develop new apparatus, construct and validate new tests,  measurement techniques, computer programs, etc., before they can even start their research.  This can add years to the project.
4. Collect data designed to test the hypothesis.  Frequently, the methods and techniques developed by the researcher don't work on the first try.  Sometimes it takes months or years of practice and refinement of the equiment, tests, or apparatus until the data can be collected successfully.
5. Analyzie the data.
6. Write up the results for publication

Science is Competitive

Publish Or Perish Environment

    Scientists work in a publish or perish environment.  All scientists must conduct new and original research and publish the results regularly in order to keep their jobs, get raises, or be eligible for promotions.  Scientists are constantly looking for new things to research.

    Coming up with new research projects is extremely difficult.  If a scientist must publish 2 or 3 articles a year and it takes 3 to 6 years to get each article, the scientist and his students must have 6 to 12 projects going at all times. 
 

Peer Reviewed

    In order to get an article published, the project must be reviewed by a panel of other scientists who check the work to be sure every step has been properly followed, that each conclusion is justified, that the explanation offered by the author is the best explanation of the data, etc.  Frequently, the panel reviewing the article includes scientists who are on the other side of the issue.  Editors deliberately send an article to reviewers who are likely to disagree with the conclusions since they are most likely to find flaws in the project.

    The critical thing is that each project must be reviewed by knowledgable scientists who know the theories, know the methods, know the data, and are in a position to determine if the conclusions in the article are justified by the data.

Self Correcting

    No scientific finding is accepted after only one research project.  When a researcher publishes a finding, scientists at other laboratories are quick to "replicate" or repeat the study to verify that they get the same result.  Many scientists run several replications of their own studies to verify that they can get the same result at least 3 times in a row before they will send the results off for publication.

    The easiest way to get a publication is to find an error in someone elses research, repeat their research correcting the error.  The other researcher has already reviewed the literature, generated the hypothesis, developed the methods, and done all the hard and slow stuff.  All you have to do is correct the flaw in their research method, collect new data, analyze it, and write it up.  This can still take a couple of years but it is quicker than starting from scratch.

    One of the surest ways to get a publication is to prove some other researcher wrong.  One of the quickest ways to develop a national reputation (ie:get famous) is to prove that some well known theory is wrong.  That will quickly guarantee the scientist a raise and a promotion.

    As soon as an article is published in a scientific journal, a dozen other scientists in a dozen other laboratories are all over it "like white on rice" looking for flaws and errors so they can get a quick publication by proving it wrong.

    So while sometimes, scientific methods lead to wrong conclusions, within a couple of years of publishing them, they are usually corrected.  In some cases, wrong conclusions cannot be disproved until some new method is invented.  The invention of the laser, for example, alowed us to re-evaluate a number of hypotheses that could not be properly tested until the laser was invented. 
 

Based on High Ethical Standards

    Scientists are held to the highest ethical standards.  A scientist engaging in dishonest or unethical behavior will lose his or her job, reputation, and credentials as a scientist.  Scientists reviewing other scientists research look for flaws in the method and flaws in the logic but they do not reject an article just because it disagrees with their own favorite theory.  Scientists encourage the development of competing theories because it leads to advancement in their field of research. 
 

Science Works

    Because of the self correcting structure of the scientific method, science works.  False conclusions can be part of science for years but eventually they are identified and corrected.

    Science works but it works slowly.

    The advancements of science and technology have revolutionized life on this planet.

    Unfortunately, the media do not understand science very well.  When a new finding is published, the media are quick to put out a headline to the effect that "Scientist report yada yada yada"  then two years later when the first follow up studies are published, the media is quick to report "Scientists reverse earlier conclusions, now they say yada yada yada."  This makes it sound like scientists can't make up their mind, that once they say one thing then they say the opposite.  Some people even say things like, "You can prove anything with science."  Of course that is simply not true and it is based on a misunderstanding of the slow, self-correcting, method used in science.

Relative age dating--determine whether the rock is older or younger than other rocks relative to one another

Absolute age dating--use radiometric dating techniques to determine how old rock is in the exact number of years

Not all rocks can be dated absolutely, so combinations of techniques are used. By examining layers of sedimentary rock, geologists developed a time scale for dividing up earth history.

Early in the 20thcentury, radiometric-dating techniques allowed scientists to put absolute dates on divisions in the geologic time scale.

So, what is Absolute Age Dating?

• Uses radiometric Dating Techniques
• Use naturally-occurring radioactive isotopes
• Isotope: form of an element that has additional neutrons
• Radioisotope --isotope that spontaneously decays, giving off radiation

Rate of Radioactive Decay is important:

• Radioisotopes decay at a constantrate.
• Rate of decay is measured by half-life
• Half-life: time it takes for one-half of the radioactive material to decay.

Decay products

• Radioisotopes may decay to form a different isotope or a stable isotope. 
• Stable isotope is called the "daughter" formed from decay of radioactive "parent"

Exactly how is this accomplished?

• Radioisotopes are trapped in minerals when they crystallize.
• Radioisotopes decay through time, and stableisotopes are formed.
• Scientists determine the ratioof parent isotope to daughter product which reveals the number of half-lives that has elapsed.

What does our text mean by "Earth Science"?

The theory that all geologic phenomena may be explained as the result of existing foreces having operated uniformly from the origin of the earth to the present time. 

uniformitarianism,  in geology, the doctrine that existing processes acting in the same manner and with essentially the same intensity as at present are sufficient to account for all geologic change. Uniformitarianism posits that natural agents now at work on and within the Earth have operated with general uniformity through immensely long periods of time.

The principle of uniformity postulates that phenomena displayed in the rocks may be entirely accounted for by geologic processes that continue to operate at the present day—in other words, the present is the key to the past. This principle is fundamental to geologic thinking and underlies the whole development of the science of geology. 

Physical geology is the study of the Earth's features and how they are formed. Such as the rock cycle, water cycle, erosion, etc. 

Historical geology is the study of the Earth's physical geologic features and the evolution of the life change through a time line (from the Haden to the Cenozioc). The history of the Earth. 

(1) physical geology, and (2) historical geology. Physical geology is the study of Earth materials (rocks and minerals) and processes (volcanism, earthquakes, plate tectonics, etc.).

Historical geology is obviously the study of Earth history.

The distinction between physical and historical geology is really somewhat artificial anyway, because knowledge of Earth processes is necessary to understand Earth history, and knowledge of Earth‟s history gives better insight into the processes that continue to shape our planet today.