View images by clicking on link or reduced image: Each image opens into a new window. These primitive, medium sized apes lived in rain forests between 18 and 22 million years ago. This species and others such as Dryopithecus existed before the hominid line diverged on the path to humans. This lineage ancestral gibbons is believed to have diverged from the great ape and human lineages between 17 and 25 Mya Avers, Oreopithecus ‘s hand closely matches the pattern of early hominids, with a grasping capability including firm pad-to-pad precision gripping that apes are unable to perform presumably as a response to similar functional demands to hominids Moya-Sola et al, Bipedal activities made up a significant part of the positional behavior of this primate Kohler and Moya-Sola, Gorilla and human DNA only differs by 2. Our DNA differs by only 1.
Abstract This paper presents a review of available petrological, geochonological and geochemical data for late Mesozoic to Recent igneous rocks in the South China Sea SCS and adjacent regions and a discussion of their petrogeneses and tectonic implications. The integration of these data with available geophysical and other geologic information led to the following tectono-magmatic model for the evolution of the SCS region.
These granitoids were formed in a continental arc tectonic setting, consistent with the ideas proposed by Holloway and Taylor and Hayes , , that there existed an Andean-type volcanic arc during later Mesozoic era in the SCS region. The geodynamic setting of the earlier volcanics was an extensional regime, which resulted from the collision between India and Eurasian plates since the earliest Cenozoic, and that of the post-spreading volcanics may be related to mantle plume magmatism in Hainan Island.
In addition, the nascent Hainan plume may have played a significant role in the extension along the northern margin and seafloor spreading in the SCS.
Summary. The conventional K-Ar dating method was applied to the dacite flow from the new lava dome at Mount St Helens, Washington. Porphyritic dacite which solidified on the surface of the lava dome in gives a whole rock K-Ar ‘age’ of ± million years (Ma).
Fission track analysis Radiocarbon Dating Carbon is a very special element. In combination with hydrogen it forms a component of all organic compounds and is therefore fundamental to life. Libby of the University of Chicago predicted the existence of carbon before it was actually detected and formulated a hypothesis that radiocarbon might exist in living matter.
Willard Libby and his colleague Ernest Anderson showed that methane collected from sewage works had measurable radiocarbon activity whereas methane produced from petroleum did not. Perseverance over three years of secret research to develop the radiocarbon method came into fruition and in Libby received the Nobel Prize for chemistry for turning his vision into an invaluable tool. The basic principle Carbon has three naturally occurring isotopes , with atoms of the same atomic number but different atomic weights.
They are 12C, 13C and 14C. C being the symbol for carbon and the isotopes having atomic weights 12, 13 and
Unreliability of Radiometric Dating and Old Age of the Earth
The Potassium Argon Reaction Ar 40 is used for several reasons. First of all, Argon is inert. It does not chemically react with other elements at all. So Argon does not attach itself to the rock or any minerals in the rock. Secondly, Argon is usually a gas. These features are thought to allow any naturally occurring Argon from contaminating our measurements of the Argon 40 that is being produced from the radioactive decay of K
The K-Ar method is probably the most widely used radiometric dating technique available to geologists. It is based on the radioactivity of 40 K, which undergoes dual decay by electron capture to 40 Ar and by beta emission to 40 Ca.
Carbon 14 is used for this example: This nullifies the carbon method as well as demonstrating that the earth is less than 10, years old. The above is offered as a simple fact of research. Knowing how faulty creationist “facts” can be, let’s do a little research of our own. One suspects that the scientific world would not be using the carbon method if it were so obviously flawed.
Could it be that the whole scientific community has missed this point, or is it another case of creationist daydreaming? This argument was popularized by Henry Morris , p.
This is very possible, and even likely. It is only an assumption that integral or adjacent lead could only be an end-product. In addition, there is “common lead, “which has no radioactive parent lead This could easily be mixed into the sample and would seriously affect the dating of that sample. Faul, an authority in the field, recognized it also: When the earth’s crust was formed, the primordial lead was frozen into rocks that also contained uranium and thorium in various ratios to lead.
The location of the center is difficult to estimate, but would be near the present summit, based on the lava distribution. The edifice would be like a small shield in shape with gentle slope. On the other hand, the late period is characterized by the repeated effusion of relatively viscus andesitic to dacitic lava. As a result, cone shaped edifice would be formed.
K-Ar data of 0. The former is from lower part of the Gassan lower lavas, whereas the latter is from upper part of them. Based on the former age, it is reasonable to consider that the early period would start around 0.
Chronological Methods 9 – Potassium-Argon Dating Potassium-Argon Dating Potassium-Argon dating is the only viable technique for dating very old archaeological materials. Geologists have used this method to date rocks as much as 4 billion years old. It is based on the fact that some of the radioactive isotope of Potassium, Potassium K ,decays to the gas Argon as Argon Ar By comparing the proportion of K to Ar in a sample of volcanic rock, and knowing the decay rate of K , the date that the rock formed can be determined.
How Does the Reaction Work?
The decay rate and therefore the half-life are fixed characteristics of an isotope. They don’t change at all. That’s the first axiom of radiometric dating techniques: the half-life of a given isotope is a constant. By K-Ar dating, the volcanic rock that forms Midway’s core is million years old. Radiometric dating has been used ever.
We can calculate the half-lives of all of these elements. All the intermediate isotopes between U and Pb are highly unstable, with short half-lives. That means they don’t stay around very long, so we can take it as given that these isotopes don’t appear on Earth today except as the result of uranium decay. We can find out the normal distribution of lead isotopes by looking at a lead ore that doesn’t contain any uranium, but that formed under the same conditions and from the same source as our uranium-bearing sample.
Then any excess of Pb must be the result of the decay of U When we know how much excess Pb there is, and we know the current quantity of U , we can calculate how long the U in our sample has been decaying, and therefore how long ago the rock formed. Th and U also give rise to radioactive series — different series from that of U , containing different isotopes and ending in different isotopes of lead.
Chemists can apply similar techniques to all three, resulting in three different dates for the same rock sample. Uranium and thorium have similar chemical behavior, so all three of these isotopes frequently occur in the same ores. If all three dates agree within the margin of error, the date can be accepted as confirmed beyond a reasonable doubt. Since all three of these isotopes have substantially different half-lives, for all three to agree indicates the technique being used is sound.
But even so, radioactive-series dating could be open to question. It’s always possible that migration of isotopes or chemical changes in the rock could yield incorrect results. The rock being dated must remain a closed system with respect to uranium, thorium, and their daughter isotopes for the method to work properly.
The Radiometric Dating Game
I was born and raised in Vermont. Applications have largely focused on questions in paleoanthropology and the geologic timescale. Journal of Analytical Atomic Spectrometry. Elemental, isotopic, and geochronological variability in Mogollon-Datil volcanic province archaeological obsidian, southwestern USA: Solving issues of inter-source discrimination.
The conventional K-Ar dating method depends on the assumptions that the sample contained no Ar at the time of its formation and all the radiogenic Ar produced within it was quantitatively retained (Faure and Mensing ). “Determination of the Radioisotope Decay Constants and Half-lives: Rubidium (87 Rb “Determination of the.
Preliminary papers in the late s suggested either Zhamanshin  or Elgygytgyn  as the source of the Australasian strewnfield. Povenmire and others have proposed the existence of an additional tektite strewn field, the Central American strewn field. Evidence for this reported tektite strewn field consists of tektites recovered from western Belize in the area of the villages of Bullet Tree Falls, Santa Familia and Billy White.
A limited amount of evidence is interpreted as indicating that the proposed Central American strewn field likely covers Belize, Honduras, Guatemala, Nicaragua and possibly parts of southern Mexico. It is speculated that the hypothesized Pantasma Impact Crater in northern Nicaragua might be the source of these tektites. Similar agreements exist between tektites from the North American strewnfield and the Chesapeake Bay impact crater and between tektites from the Ivory Coast strewnfield and the Lake Bosumtwi Crater.
Ages of tektites have usually been determined by either the K-Ar method, fission-track dating, the Ar-Ar technique, or combination of these techniques. During the extreme conditions created by an hypervelocity meteorite impact, near-surface terrestrial sediments and rocks were either melted, vaporized, or some combination of these and ejected from an impact crater. After ejection from the impact crater, the material formed millimeter- to centimeter-sized bodies of molten material, which as they re-entered the atmosphere, rapidly cooled to form tektites that fell to Earth to create a layer of distal ejecta hundreds or thousands of kilometers away from the impact site.
The chemical and isotopic composition of tektites indicates that they are derived from the melting of silica-rich crustal and sedimentary rocks , which are not found on the Moon. In addition, some tektites contain relict mineral inclusions quartz , zircon , rutile , chromite , and monazite that are characteristic of terrestrial sediments and crustal and sedimentary source rocks.
Also, three of the four tektite strewnfields have been linked by their age and chemical and isotopic composition to known impact craters.
The Element Calcium
Acknowledgements Introduction his document discusses the way radiometric dating and stratigraphic principles are used to establish the conventional geological time scale. It is not about the theory behind radiometric dating methods, it is about their application, and it therefore assumes the reader has some familiarity with the technique already refer to “Other Sources” for more information. As an example of how they are used, radiometric dates from geologically simple, fossiliferous Cretaceous rocks in western North America are compared to the geological time scale.
To get to that point, there is also a historical discussion and description of non-radiometric dating methods. A common form of criticism is to cite geologically complicated situations where the application of radiometric dating is very challenging. These are often characterised as the norm, rather than the exception.
Leaching experiments suggest that K, Ar, Rb, and Sr in exchangeable and nonexchangeable sites of the structure of stoichiometric celadonite maintain their isotope characteristics and are resistant to change from diagenetic processes or surface alteration.
See some updates to this article. We now consider in more detail one of the problems with potassium-argon dating, namely, the branching ratio problem. Here is some relevant information that was e-mailed to me. There are some very serious objections to using the potassium-argon decay family as a radiometric clock. The geochronologist considers the Ca40 of little practical use in radiometric dating since common calcium is such an abundant element and the radiogenic Ca40 has the same atomic mass as common calcium.
Here the actual observed branching ratio is not used, but rather a small ratio is arbitrarily chosen in an effort to match dates obtained method with U-Th-Pb dates. The branching ratio that is often used is 0. Thus we have another source of error for K-Ar dating. Back to top Thus there are a number of sources of error. We now consider whether they can explain the observed dates.
In general, the dates that are obtained by radiometric methods are in the hundreds of millions of years range. One can understand this by the fact that the clock did not get reset if one accepts the fact that the magma “looks” old, for whatever reason. That is, we can get both parent and daughter elements from the magma inherited into minerals that crystallize out of lava, making these minerals look old.
Since the magma has old radiometric dates, depending on how much the clock gets reset, the crust can end up with a variety of younger dates just by partially inheriting the dates of the magma.
What is Carbon (14C) Dating Carbon Dating Definition
Collins January Introduction The creationists are asking for equal time in science classrooms to teach that the Genesis stories are valid scientific interpretations of earth history. Equal time for creationists’ interpretations are not likely to occur in secular universities and schools, but if the creationist are serious about equal time, then they should be open to granting equal time in their private Christian schools for presentations of both sides of a scientific issue a literalist biblical view and the modern science view.
The origin, age, and other characteristic features of granite are such issues deserving equal time. If I were given equal time in a science classroom at a private, fundamentalist, Christian college or secondary school, advocating creationists’ views, the following would be the kinds of information that I would provide for a modern scientific interpretation of granite to compare with the corresponding creationists’ biblical interpretation.
Furthermore, since K-Ar dating gives the same length to this record we have no reason for not trusting within a few percent the K-Ar absolute age for this stratum, which is about million years. Well, Bob?
Departures from this assumption are quite common, particularly in areas of complex geological history, but such departures can provide useful information that is of value in elucidating thermal histories. A deficiency of 40 Ar in a sample of a known age can indicate a full or partial melt in the thermal history of the area. Reliability in the dating of a geological feature is increased by sampling disparate areas which have been subjected to slightly different thermal histories.
Ar—Ar dating is a similar technique which compares isotopic ratios from the same portion of the sample to avoid this problem. Applications[ edit ] Due to the long half-life , the technique is most applicable for dating minerals and rocks more than , years old. For shorter timescales, it is unlikely that enough 40 Ar will have had time to accumulate in order to be accurately measurable. K—Ar dating was instrumental in the development of the geomagnetic polarity time scale.
One archeological application has been in bracketing the age of archeological deposits at Olduvai Gorge by dating lava flows above and below the deposits. In the K—Ar method was used by the Mars Curiosity rover to date a rock on the Martian surface, the first time a rock has been dated from its mineral ingredients while situated on another planet.