Sedimentary Rocks Formation and Fossils!

This belief in long ages for the earth and the existence of life is derived largely from radiometric dating. These long time periods are computed by measuring the ratio of daughter to parent substance in a rock and inferring an age based on this ratio. This age is computed under the assumption that the parent substance say, uranium gradually decays to the daughter substance say, lead , so the higher the ratio of lead to uranium, the older the rock must be. Of course, there are many problems with such dating methods, such as parent or daughter substances entering or leaving the rock, as well as daughter product being present at the beginning. Here I want to concentrate on another source of error, namely, processes that take place within magma chambers. To me it has been a real eye opener to see all the processes that are taking place and their potential influence on radiometric dating. Radiometric dating is largely done on rock that has formed from solidified lava. Lava properly called magma before it erupts fills large underground chambers called magma chambers. Most people are not aware of the many processes that take place in lava before it erupts and as it solidifies, processes that can have a tremendous influence on daughter to parent ratios. Such processes can cause the daughter product to be enriched relative to the parent, which would make the rock look older, or cause the parent to be enriched relative to the daughter, which would make the rock look younger.


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.

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Thus we do not know the numeric age of any given layer. The civilizations that deposited the trash had a culture and industrial capabilities that evolved through time. The oldest inhabitants used primitive stone tools, later inhabitants used cups made of ceramics, even later inhabitants eventually used tin cans and then changed to Aluminum cans, and then they developed a technology that used computers. This shows that society has evolved over the years.

Similar cultures must have existed in both areas and lived at the same time. Thus we can make correlations between the layers found at the different sites by reasoning that layers containing similar distinctive discarded items artifacts were deposited during the same time period.

Relative and absolute ages in the histories of Earth and the Moon: The Geologic Time Scale

The Geologic Time Scale A few days ago, I wrote a post about the basins of the Moon — a result of a trip down a rabbit hole of book research. Here’s the next step in that journey: In the science of geology, there are two main ways we use to describe how old a thing is or how long ago an event took place.

There are absolute ages and there are relative ages. People love absolute ages.

Luminescence dating (including thermoluminescence and optically stimulated luminescence) is a type of dating methodology that measures the amount of light emitted from energy stored in certain rock types and derived soils to obtain an absolute date for a specific event that occurred in the past.

Art Rocks in Saudi Arabia “Jubbah is one of the most curious places in the world, and to my mind one of the most beautiful,” wrote Lady Anne Blunt. The granddaughter of Lord Byron had arrived in January with her husband, Wilfrid, at the oasis two-thirds of the way across the Nafud desert. En route to the city of Hail to see, and perhaps buy, some of the famous horses of Ibn Rashid, then ruler in Najd, they were among the first travelers from the West to set foot in Jubbah.

Although not geologists, they recognized that the plain, more than 16 kilometers long and five kilometers wide 10 x 3 mi —”a great bare space fringed by an ocean of sand” and overlooked by a sandstone massif”—was the site of a former lake. Among the rocks, Wilfrid found inscriptions. They had been on the lookout for traces of ancient writing, but had “hitherto found nothing except some doubtful scratches, and a few of those simple designs one finds everywhere on the sandstone, representing camels and gazelles.

Anything else they found unworthy of attention. But attitudes have changed. Today, rock art is recognized as sophisticated, complex and esthetically interesting evidence of how early humans socialized their landscapes. Pictures carved or pecked into rock speak to us all, however faintly or incomprehensibly, across great divides of time, and appeal powerfully to our imaginations. According to Paul Bahn, a leading scholar of prehistoric art, it “gives humankind its true dimension” by showing that even from the earliest times, “human activities hold meanings other than those of a purely utilitarian kind.

The parade of images and elaborate symbols, left there by successive prehistoric nomadic and settled groups, leads up to more recent written inscriptions that lie on the horizon of history. These located and recorded thousands of images and inscriptions, and they proved that the Jubbah site did indeed lie on an ancient lakebed stretching eastward from the sandstone mountain called Jabal Um Sanaman, “Two Camel-Hump Mountain.

Relative Dating

Mineralogy As a discipline, mineralogy has had close historical ties with geology. Minerals as basic constituents of rocks and ore deposits are obviously an integral aspect of geology. The problems and techniques of mineralogy, however, are distinct in many respects from those of the rest of geology, with the result that mineralogy has grown to be a large, complex discipline in itself. Nepheline greasy light gray , sodalite blue , cancrinite yellow , feldspar white , and ferromagnesian minerals black in an alkalic syenite from Litchfield, Maine, U.

About 3, distinct mineral species are recognized, but relatively few are important in the kinds of rocks that are abundant in the outer part of the Earth. Thus a few minerals such as the feldspars, quartz, and mica are the essential ingredients in granite and its near relatives.

Unfortunately, those methods don’t work on all rocks, and they don’t work at all if you don’t have rocks in the laboratory to age-date. There’s no absolute age-dating method that works from orbit, and although scientists are working on age-dating instruments small enough to fly on a lander (I’m looking at you, Barbara Cohen), nothing has.

The principle states that in a sequence of undeformed sedimentary rocks the oldest beds are at the bottom and the youngest ones are at the top. Underlying assumptions are 1 that layers were originally deposited horizontally, 2 and that beds are not overturned sedimentary structures can be used to dermine whether a sedimentary succession is overturned or not. More on index fossils here. Faunal Succession is based on the observation that animals and animal communities that are preserved in sedimentary rocks change noticeably as geologic time passes evolution.

It was first recognized by William Smith, a British Surveyor, who while working on open cuts of canals, railroads, and roads, noticed that the fossils change systematically from the older towards the younger rocks. This principle has in the meanwhile been established to be true for all sediments worldwide, and is the basis of worldwide correlation of sedimentary rock units and one of the underpinnings of the theory of evolution. The image at left illustrates faunal succession. In location A we have rock layers that successively have different types and combinations assemblages of fossils.

If in location B we find the same fossil assemblage Assemblage 2 in a rock unit, we may assume that they are of essentially the same age as in location A. Obviously, the sedimentary rocks had to be there prior to emplacement of the igneous rocks, and thus they are older than the igneous rocks. Conversely, the igneous rocks are younger than the sedimentary rocks. Other examples of cross crutting relationships can be related to faults fault has to be younger than the rock it is found in and unconformities see below.

Inclusions are always older than the rock they are found in.

Mechanical Weathering

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.

Among many methods, carbon dating is most commonly used to date fossils. In carbon dating, scientists look at how much carbon is left in the fossil, look at the half-life period, and use that to see when it was from.

What do scientist use to date the exact age of fossils? The major element in anything living or dead is Carbon, C. Carbon usually exists as the isotope C 12 meaning that it has 6 protons and 6 neutrons in its nucleus. However, a small percentage of all C exists as the radioactive C 14 isotope. This isotope has a half life of around years if my GCSE… Physics memory bank serves me correctly!

Scientists work out how strong the radioactivity of a specimen such as a fossil is my probably using equipment such as sensitive Geiger counters and oscilloscopes to measure the strength of the radiation. The weaker the signals, the older the specimen or so I believe. Placing this question in Archaeology or Physics may bring out a more detailed answer.

They use Carbon Dating.

Geologic Time

Paleomagnetic dating[ edit ] A sequence of paleomagnetic poles usually called virtual geomagnetic poles , which are already well defined in age, constitutes an apparent polar wander path APWP. Such path is constructed for a large continental block. APWPs for different continents can be used as a reference for newly obtained poles for the rocks with unknown age.

For paleomagnetic dating it is suggested to use the APWP in order to date a pole obtained from rocks or sediments of unknown age by linking the paleopole to the nearest point on the APWP. Two methods of paleomagnetic dating have been suggested 1 Angular method and 2 Rotation method.

Geology dating science to establish the age of a rock or a fossil, geology what two methods are used to determine the age of a rock or fossil dating science researchers use some type of relative dating examples clock to determine the date it was radiometric dating methods, based.

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.

FAQ – Radioactive Age-Dating

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.

Radioactive dating uses the decay rates of radioactive substances to measure absolute ages of rocks, minerals and carbon-based substances, according to How Stuff Works. Scientists know how quickly radioactive isotopes decay into other elements over thousands, millions and even billions of years.

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.

1.6 Absolute Dating of Rocks