Another “A” paper.

Radiocarbon Dating

Have you ever taken a nature hike through the woods and found a fossil or ancient artifact and wondered exactly how old it was? You can look at it skeptically and try to determine how old it looks or from what time period it came, but you cannot be sure your guesses are accurate. Willard F. Libby, an American chemist in the late 1940’s, developed a technique to determine the age of ancient objects by measuring the radiocarbon content in them (Berger). This technique is called radiocarbon dating. The technique has been used by archaeologists and geologist ever since. The process is not too complicated, and, if explained well, should easily be comprehended and understood.

This is a wonderful descriptive thesis.  I like the introduction too.  It ties the subject in to things that may be interesting to the reader.

To understand the radiocarbon dating process, it is useful to know some important information about carbon. Carbon has a radioactive isotope with an atomic weight of 14 atomic mass units (amu), which is heavier than the common carbon isotope with an atomic weight of 12 amu. This radioactive isotope of carbon is called radiocarbon, or Carbon 14 (Berger) This radiocarbon is what scientists have used to “determine the age of fossils and other kinds of ancient objects” (Berger).  None of the references so far are really necessary.  The fact that carbon-14 is radioactive and used to date things is common knowledge, and so doesn’t need to be referenced.  Quotes should only be used for emphasis.

Rainer Berger’s article entitled “Radiocarbon” from World Book helps to explain the following principles related to radiocarbon: the formation of radiocarbon comes from high- energy atomic particles called “cosmic rays” when they smash into the earth’s atmosphere. “Cosmic rays cause atoms in the atmosphere to break down into electrons, neutrons, protons, and other particles” Some neutrons happen to strike the nuclei of nitrogen atoms in our atmosphere. Each of these nuclei absorbs a neutron and loses a proton, so this nitrogen atom becomes a radiocarbon atom.  This is important information, but the transition is a bit rough.  Organizationally it would be better to build a need for the information before supplying it. 

There are several radioactive dating processes, but the process most commonly used to determine the age of ancient objects is radiocarbon dating. This technique is used by measuring the radiocarbon content in an object. Archeologists and geologists have been able to learn a lot about “prehistoric human beings, animals, and plants that lived up to 50,000 years ago” (Berger).   The order of the last 3 paragraphs could be better.  This last paragraph is a restatement of the 2^nd paragraph.

Every living thing contains radiocarbon. “In the atmosphere, there is about one radiocarbon atom for every trillion molecules of carbon dioxide gas” (Berger). Plants take in radiocarbon from the carbon dioxide in the air. We as human beings receive our radiocarbon mainly from our food. The radiocarbon in our food, initially, came from plants. Either we eat the plants directly and take in radiocarbon from them or we eat animals, which received radiocarbon by eating the plants themselves.

“Radiocarbon atoms, like all radioactive substances, decay (break down by releasing particles) at an exact and uniform rate” (Berger). Radiocarbon has a half-life of about 5,730 years. This means that half of the radiocarbon decays, turning back into nitrogen, in that amount of time. In another 5,730 years half of the half would be left, or a fourth of the original amount of radiocarbon would be decayed. In each 5,730 years the amount of radiocarbon is cut in half from what it was previously. The amount of radiocarbon never reaches zero because it is only cut in half. You start out with a certain amount of radiocarbon and then, in 5,730 years, you have half of the original and then, in 11,460 year, a fourth of the original, then, in 17,190 years, an eighth of the original and then, in 22,920 years, a sixteenth of it will remain and soon. It is apparent that the amount never reaches zero; it just gets extremely close after tens of thousands of years.

Living organisms have radiocarbon in their tissues that decays extremely slowly but is continuously renewed while the organism is still living. Organisms continue to eat plants and animals taking in additional radiocarbon constantly. When an organism dies, it no longer replenishes its radiocarbon supply and the radiocarbon currently in its tissues continues to decrease at a constant rate (Berger). “This steady decay at a known rate—a half-life of approximately 5,730 years—enables scientists to determine an objects’ age” (Berger).

There are two methods of actually finding the radiocarbon content in objects. In the first method, the scientists burn a piece of the object to convert it to carbon dioxide gas (Berger). They purify the carbon dioxide and measure the amount of radiocarbon in the purified carbon dioxide with radiation counters. Radiation counters are “instruments (that detect the electrons released by the radiocarbon atoms as the atoms change back into nitrogen atoms” (Berger) The number of electrons that are emitted indicates the radiocarbon content. The second method of radiocarbon dating uses certain types of particle accelerators instead of radiation counters. The accelerators help scientists to “detect and count directly the individual radiocarbon atoms in an extremely small portion of an object” (Berger). Once the radiocarbon content is known, scientists compare that number with the radiocarbon content in tree rings whose ages are known (Berger). At different times in the past there have been small variations of the radiocarbon content in the atmosphere. By comparing to the radiocarbon content in tree rings) scientists can compensate for these variations and convert the object’s age more precisely to a specific date (Berger).

 “Archaeology,” an article by Thomas R. Hester, is where the following information came from: “Dating of archaeological objects is called archaeometry. The methods of archaeometry are divided into two major types: (I) relative dating and (2) absolute dating” (Hester). Information about the age of an object in relation to other objects is relative dating. Relative dating does not produce any dates of how old an object is; it gives comparisons to other objects. Absolute dating determines the objects age in numbers years since it has been living.  Therefore, absolute dating gives more exact dates of how old an object is; it does more than just relate it to other old objects.  I’m not sure that this information fits in in the paper.  The whole paper is about radiocarbon dating, an absolute dating method.  This paragraph could be used toward the front of the paper to distinguish radiometric dating from other types of dating, but it seems out of place here.

There are different dating methods depending on the object being dated. Radiocarbon dating is the most widely used dating method. There are, actually, two types of radiocarbon dating available for use today. Traditional radiocarbon dating requires several grams of organic material but is less expensive to perform. Accelerator mass spectrometry dating needs only a small sample of an artifact or a small amount of organic material. Other types of dating are used more specifically for certain objects. If you found rocks associated with fossils of early human ancestors in Africa, you would use potassium-argon dating. There are other types of dating like electron spin resonance, uranium-series dating, and obsidian-hydration dating used in special cases when radiocarbon dating cannot be used.  Once again, discussing the different types of radioactive dating should have been done before discussing some of the details of carbon dating, if at all.  Potassium argon dating really is not important to the thesis, and the description of the two types of radiocarbon dating would fit better in the paragraph before last.

In 1952, Willard F. Libby, the chemist who discovered radiocarbon dating, wrote about the limitations of the method he came up with and the conditions under which his figures would be valid (Kogan). The following limitations came from an online website containing an article called, “The Pitfalls of Radiocarbon Dating:” the first limitation has to do with the three reservoirs of radiocarbon on earth—the atmosphere, the biosphere, and the hydrosphere. The last, the hydrosphere, is the richest; it includes the oceans and seas. Radiocarbon dating of objects from the hydrosphere is only correct if in the last 40 or 50 thousand years the quantity of water and amount of carbon diluted in it have not changed substantially. The second limitation is that the radiocarbon dating method depends on the condition that the influx of cosmic rays or energy particles coming from the stars and the sun has not suffered variations. Assumptions are that both of these limitations are true and that enables us to continue to use this radiocarbon dating method. If either of these limitations turned out to be false, (if the carbon diluted in the water did change or if the influx of cosmic rays was not constant ) radiocarbon dating would no longer be accurate.  This could be explained in more detail.

Radiocarbon dating is very useful to determine how old artifacts are. There are many important discoveries that have been dated. Archaeologists have been able to date these discoveries. Some examples of ancient artifacts that archaeologists have been able to date are mummies, fossils, people found in glaciers, and the Dead Sea Scrolls.

The Dead Sea Scrolls, a collection of 2,000 complete and fragmented manuscripts, were discovered,. in caves along the shore of the Dead Sea the late 1940’s and early 1950’s ‘ (Archaeology). The Dead Sea Scrolls contain all of the books of the Old Testament excluding Ester. In July of 1991 the results of a radiocarbon dating test on the Dead Sea Scrolls were reported (Archaeology). “The tests confirmed that the scrolls date from the mid-100’s B.C. to the late first century AD.” (Archaeology). This helped people to see the validity of the scrolls by proving that they were written when people thought they should have been written. Without radiocarbon dating, people would not have known if the scrolls were real or fake. They could have assumed that they were old by how they “looked” or based on the writing styles used in them. Nobody could have said with absolute certainty that the scrolls came from the time period they actually were from. Radiocarbon dating made that validity possible.

In September 199!, the preserved body of a man was discovered in a glacier in northeastern Italy (Archaeology). The man was found with an ax, a bow, 14 arrows, a flint knife, flint and tinder in a leather pouch, and a woven mat (Archaeology). Scientists were able to obtain radiocarbon dates from pieces of grass taken from the woven mat found with the man (Archaeology). They were able to determine the man died at least 4,600 years ago (Archaeology). “The body and the objects found with it represent the most complete archaeological find from the late Neolithic Period (New Stone Age) in Europe” (Archaeology). Scientists are able to learn about our history through finding and dating things, like this human body. Scientists can date this man to find out when he lived and then, they can learn about him and discover things about how the world was at that point in time. They can learn things about how his civilization was, methods he used to obtain food, ways he started fires, and his sleeping conditions. This man was a very important discovery.  I would have preferred to see the process described in detail for one example rather than a list of examples without the process.  The thesis is about the process, not the applications.

Radiocarbon dating is a very important process that was discovered. It continues to prove its value through the artifacts it has dated, does date, and will date in the future. Scientists have been able to learn an incredible amount about our early world, which they could not have known before, through the discoveries made by radiocarbon dating. We now know things about our ancient ancestors that we would not have been able to know before. We understand how they lived and in what ways they progressed throughout the centuries. Scientists have been able to put discoveries in order from most recent to most ancient since they know exactly when they came from. The world today is indebted to Willard F. Libby for discovering the methods to radiocarbon dating.  I like the conclusion.

Score 48/50