Introduction to Geology Chapter 2 – Basic Geologic Principles The science of geology is founded on basic principles that are useful for making observations about the world around us. This chapter presents a mix of information that is essential fundamental to all following chapters. This chapter is an introduction to rocks and minerals, and the rock cycle. Basic chemistry is important to all sciences, especially geology! Everything around us is made of chemical compounds that have testable and identifying characteristics, allowing them to be classified, and their age determined. This also applies to rocks, minerals, and derivative materials such as sediments and soil. The chemical composition of Earth’s crust has similarities with other stony planets, with silicate-rich rocks being dominant in most locations on the surface. In addition, basic geologic principles can be applied to resolving the order of events leading to the formation of rocks and landscape features.
A Guide to Isaac Asimov’s Essays
Rubidium—strontium method The radioactive decay of rubidium 87Rb to strontium 87Sr was the first widely used dating system that utilized the isochron method. Because rubidium is concentrated in crustal rocks, the continents have a much higher abundance of the daughter isotope strontium compared with the stable isotopes.
A ratio for average continental crust of about 0. This difference may appear small, but, considering that modern instruments can make the determination to a few parts in 70, , it is quite significant. Dissolved strontium in the oceans today has a value of 0. Thus, if well-dated, unaltered fossil shells containing strontium from ancient seawater are analyzed, changes in this ratio with time can be observed and applied in reverse to estimate the time when fossils of unknown age were deposited.
Bones can’t be dated with the potassium/argon method, Bill. Only igneous rock can be dated that way. Now, parts of the geological formation in which the fossils were found have been dated by various radiometric methods, and the consensus is that the rocks themselves are million years old.
These are K-Ar data obtained on glauconite, a potassium-bearing clay mineral that forms in some marine sediment. Woodmorappe fails to mention, however, that these data were obtained as part of a controlled experiment to test, on samples of known age, the applicability of the K-Ar method to glauconite and to illite, another clay mineral.
He also neglects to mention that most of the 89 K-Ar ages reported in their study agree very well with the expected ages. Evernden and others 43 found that these clay minerals are extremely susceptible to argon loss when heated even slightly, such as occurs when sedimentary rocks are deeply buried. As a result, glauconite is used for dating only with extreme caution.
The ages from the Coast Range batholith in Alaska Table 2 are referenced by Woodmorappe to a report by Lanphere and others Whereas Lanphere and his colleagues referred to these two K-Ar ages of and million years, the ages are actually from another report and were obtained from samples collected at two localities in Canada, not Alaska. There is nothing wrong with these ages; they are consistent with the known geologic relations and represent the crystallization ages of the Canadian samples.
The Liberian example Table 2 is from a report by Dalrymple and others These authors studied dikes of basalt that intruded Precambrian crystalline basement rocks and Mesozoic sedimentary rocks in western Liberia. The dikes cutting the Precambrian basement gave K-Ar ages ranging from to million years Woodmorappe erroneously lists this higher age as million years , whereas those cutting the Mesozoic sedimentary rocks gave K-Ar ages of from to million years.
Woodmorappe does not mention that the experiments in this study were designed such that the anomalous results were evident, the cause of the anomalous results was discovered, and the crystallization ages of the Liberian dikes were unambiguously determined. The Liberian study is, in fact, an excellent example of how geochronologists design experiments so that the results can be checked and verified.
How Old is the Earth
At the time that Darwin’s On the Origin of Species was published, the earth was “scientifically” determined to be million years old. By , it was found to be 1. In , science firmly established that the earth was 3. Finally in , it was discovered that the earth is “really” 4. In these early studies the order of sedimentary rocks and structures were used to date geologic time periods and events in a relative way. At first, the use of “key” diagnostic fossils was used to compare different areas of the geologic column.
Radiometric dating or radioactive dating is a technique used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay.
Life timeline and Nature timeline Modern Awash River , Ethiopia, descendant of the Palaeo-Awash, source of the sediments in which the oldest Stone Age tools have been found The Stone Age is contemporaneous with the evolution of the genus Homo , the only exception possibly being the early Stone Age, when species prior to Homo may have manufactured tools. The closest relative among the other living primates , the genus Pan , represents a branch that continued on in the deep forest, where the primates evolved.
The rift served as a conduit for movement into southern Africa and also north down the Nile into North Africa and through the continuation of the rift in the Levant to the vast grasslands of Asia. Starting from about 4 million years ago mya a single biome established itself from South Africa through the rift, North Africa, and across Asia to modern China, which has been called “transcontinental ‘savannahstan"” recently. All the tools come from the Busidama Formation, which lies above a disconformity , or missing layer, which would have been from 2.
The oldest sites containing tools are dated to 2.
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,
martindale’s calculators on-line center archaeology, anthropology, paleoichnology – palaeoichnology – neoichnology, paleobiology – palaeobiology, paleobotany – palaeobotany, paleoclimatology – palaeoclimatology.
These formations may have resulted from carcass burial in an anoxic environment with minimal bacteria, thus slowing decomposition. Stromatolites Lower Proterozoic Stromatolites from Bolivia , South America Stromatolites are layered accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains by biofilms of microorganisms , especially cyanobacteria. While older, Archean fossil remains are presumed to be colonies of cyanobacteria , younger that is, Proterozoic fossils may be primordial forms of the eukaryote chlorophytes that is, green algae.
One genus of stromatolite very common in the geologic record is Collenia. The earliest stromatolite of confirmed microbial origin dates to 2. The most widely supported explanation is that stromatolite builders fell victims to grazing creatures the Cambrian substrate revolution , implying that sufficiently complex organisms were common over 1 billion years ago.
Factors such as the chemistry of the environment may have been responsible for changes. Cyanobacteria as well as extremophile Gammaproteobacteria are thought to be largely responsible for increasing the amount of oxygen in the primeval earth’s atmosphere through their continuing photosynthesis. Cyanobacteria use water , carbon dioxide and sunlight to create their food.
A layer of mucus often forms over mats of cyanobacterial cells. In modern microbial mats, debris from the surrounding habitat can become trapped within the mucus, which can be cemented by the calcium carbonate to grow thin laminations of limestone. These laminations can accrete over time, resulting in the banded pattern common to stromatolites.
How Old is the Earth
General considerations Distinctions between relative-age and absolute-age measurements Local relationships on a single outcrop or archaeological site can often be interpreted to deduce the sequence in which the materials were assembled. This then can be used to deduce the sequence of events and processes that took place or the history of that brief period of time as recorded in the rocks or soil.
For example, the presence of recycled bricks at an archaeological site indicates the sequence in which the structures were built.
Chapter 2: Atoms and the Periodic Table This content can also be downloaded as an printable PDF, adobe reader is required for full functionality. This text is published under creative commons licensing, for referencing and adaptation, please click here. Atomic Theory with Historical Perspectives Introduction to Elements and the Periodic Table Dmitri [ ].
If a layer, say 0. Considering that good satellite data on meteoritic influx were available before Morris 92 and Slusher published their papers, they obviously have been highly selective in their choice of obsolete data. A more fundamental point, however, is that such calculations are based on faulty premises, including the erroneous assumptions that the meteoritic influx has remained constant for 4. Apparently, Morris and Parker 97 have credited Slusher with a calculation that he did not do.
Table 10 , no. Morris 92 notes that intrusive rocks are much more common than lava flows: Thus, the entire crust could have been formed by volcanic activity at present rates in only million years, which would only take us back into the Cambrian period. The uniformitarian model once again leads to a serious problem and contradiction.
Radioactive decay[ edit ] Example of a radioactive decay chain from lead Pb to lead Pb. The final decay product, lead Pb , is stable and can no longer undergo spontaneous radioactive decay. All ordinary matter is made up of combinations of chemical elements , each with its own atomic number , indicating the number of protons in the atomic nucleus. Additionally, elements may exist in different isotopes , with each isotope of an element differing in the number of neutrons in the nucleus.
A particular isotope of a particular element is called a nuclide.
Dating: Dating, in geology, determining a chronology or calendar of events in the history of Earth, using to a large degree the evidence of organic evolution in the sedimentary rocks accumulated through geologic time in marine and continental environments. To date past events, processes, formations, and.
The Radiometric Dating Game Radiometric dating methods estimate the age of rocks using calculations based on the decay rates of radioactive elements such as uranium, strontium, and potassium. On the surface, radiometric dating methods appear to give powerful support to the statement that life has existed on the earth for hundreds of millions, even billions, of years.
We are told that these methods are accurate to a few percent, and that there are many different methods. We are told that of all the radiometric dates that are measured, only a few percent are anomalous. This gives us the impression that all but a small percentage of the dates computed by radiometric methods agree with the assumed ages of the rocks in which they are found, and that all of these various methods almost always give ages that agree with each other to within a few percentage points.
Since there doesn’t seem to be any systematic error that could cause so many methods to agree with each other so often, it seems that there is no other rational conclusion than to accept these dates as accurate. However, this causes a problem for those who believe based on the Bible that life has only existed on the earth for a few thousand years, since fossils are found in rocks that are dated to be over million years old by radiometric methods, and some fossils are found in rocks that are dated to be billions of years old.
If these dates are correct, this calls the Biblical account of a recent creation of life into question. After study and discussion of this question, I now believe that the claimed accuracy of radiometric dating methods is a result of a great misunderstanding of the data, and that the various methods hardly ever agree with each other, and often do not agree with the assumed ages of the rocks in which they are found.