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  • 16.01.2019
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Dating Rocks and Fossils Using Geologic Methods . Learn Science at Scitable

How do we know the age of the Earth?

Age dating the Earth Geochronology is the scientific study of the age of the Earth and the temporal sequence of events related to the formation of the planet and the history of life on Earth. The word is derived from Geo meaning Earth , and chronology , which is the study of time, or a record of events in the order of their occurrence timeline. It is from this field of study that fossils and artifacts are dated based on the perceived age of the geological layers in which they are located. Geologists determine the age of rocks , fossils , and sediments using a variety of methods including relative and absolute dating. When dating an object, a geologist measures some physical property of the object, which is believed to provide evidence regarding its age.

In a laboratory, it is possible to make a rock with virtually any composition. Ultimately, we cannot know. But there is a seemingly good reason to think that virtually all the argon contained within a rock is indeed the product of radioactive decay.

The age of the earth is normally estimated by radiometric dating - which gives an ' old earth'. What are the assumptions and weaknesses of this method?. The Age of the Earth, Dating. Methods, and Evolution. Roger Sigler, M.S.. Why is this Chapter Important? This chapter is important because an “ancient Earth” is. However, there are many methods that can be used to determine the age of the earth or other objects. The textbooks focus on relative dating.

Volcanic rocks are formed when the lava or magma cools and hardens. But argon is a gas. Since lava is a liquid, any argon gas should easily flow upward through it and escape.

Thus, when the rock first forms, it should have virtually no argon gas within it. But as potassium decays, the argon content will increase, and presumably remain trapped inside the now-solid rock. So, by comparing the argon to potassium ratio in a volcanic rock, we should be able to estimate the time since the rock formed.

This is called a model-age method. In this type of method, we have good theoretical reasons to assume at least one of the initial conditions of the rock. The initial amount of argon when the rock has first hardened should be close to zero. Yet we know that this assumption is not always true. We know this because we have tested the potassium-argon method on recent rocks whose age is historically known. That is, brand new rocks that formed from recent volcanic eruptions such as Mt.

Helens have been age-dated using the potassium-argon method. Their estimated ages were reported as hundreds of thousands of years based on the argon content, even though the true age was less than 10 years. Since the method has been shown to fail on rocks whose age is known, would it make sense to trust the method on rocks of unknown age?

But many secular scientists continue to trust the potassium-argon model-age method on rocks of unknown age. If so, then their true ages are much less than their radiometric age estimates. The age estimate could be wrong by a factor of hundreds of thousands. But how would you know? We must also note that rocks are not completely solid, but porous. And gas can indeed move through rocks, albeit rather slowly. So the assumption that all the produced argon will remain trapped in the rock is almost certainly wrong.

And it is also possible for argon to diffuse into the rock of course, depending on the relative concentration. So the system is not as closed as secularists would like to think. There are some mathematical methods by which scientists attempt to estimate the initial quantity of elements in a rock, so that they can compensate for elements like argon that might have been present when the rock first formed.

Such techniques are called isochron methods. They are mathematically clever, and we may explore them in a future article. However, like the model-age method, they are known to give incorrect answers when applied to rocks of known age.

And neither the model-age method nor the isochron method are able to assess the assumption that the decay rate is uniform. As we will see below, this assumption is very dubious. Years ago, a group of creation scientists set out to explore the question of why radiometric dating methods give inflated age estimates. We know they do because of the aforementioned tests on rocks whose origins were observed.

But why? Which of the three main assumptions initial conditions are known, rate of decay is known, the system is close is false? To answer this question, several creation geologists and physicists came together to form the RATE research initiative R adioisotopes and the A ge of T he E arth.

This multi-year research project engaged in several different avenues of study, and found some fascinating results. As mentioned above, the isochron method uses some mathematical techniques in an attempt to estimate the initial conditions and assess the closed-ness of the system.

However, neither it nor the model-age method allow for the possibility that radioactive decay might have occurred at a different rate in the past. In other words, all radiometric dating methods assume that the half-life of any given radioactive element has always been the same as it is today. If that assumption is false, then all radiometric age estimates will be unreliable.

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As it turns out, there is compelling evidence that the half-lives of certain slow-decaying radioactive elements were much smaller in the past. This may be the main reason why radiometric dating often gives vastly inflated age estimates.

Creation 101: Radiometric Dating and the Age of the Earth

First, a bit of background information is in order. Most physicists had assumed that radioactive half-lives have always been what they are today. Many experiments have confirmed that most forms of radioactive decay are independent of temperature, pressure, external environment, etc. In other words, the half-life of carbon is years, and there is nothing you can do to change it. Given the impossibility of altering these half-lives in a laboratory, it made sense for scientists to assume that such half-lives have always been the same throughout earth history.

But we now know that this is wrong.

In fact, it is very wrong. More recently, scientists have been able to change the half-lives of some forms of radioactive decay in a laboratory by drastic amounts. However, by ionizing the Rhenium removing all its electronsscientists were able to reduce the half-life to only 33 years!

In other words, the Rhenium decays over 1 billion times faster under such conditions. Thus, any age estimates based on Rhenium-Osmium decay may be vastly inflated. The RATE research initiative found compelling evidence that other radioactive elements also had much shorter half-lives in the past.

Several lines of evidence suggest this. But for brevity and clarity, I will mention only one. This involves the decay of uranium into lead Unlike the potassium-argon decay, the uranium-lead decay is not a one-step process. Rather, it is a step process.

Age of the earth dating methods

Uranium decays into thorium, which is also radioactive and decays into polonium, which decays into uranium, and so on, eventually resulting in lead, which is stable. Eight of these fourteen decays release an alpha-particle: the nucleus of a helium atom which consists of two protons and two neutrons. The helium nucleus quickly attracts a couple of electrons from the environment to become a neutral helium atom.

So, for every one atom of uranium that converts into lead, eight helium atoms are produced. Helium gas is therefore a byproduct of uranium decay. And since helium is a gas, it can leak through the rocks and will eventually escape into the atmosphere.

The RATE scientists measured the rate at which helium escapes, and it is fairly high. Therefore, if the rocks were billions of years old, the helium would have had plenty of time to escape, and there would be very little helium in the rocks. However, the RATE team found that rocks have a great deal of helium within them. In fact, the amount of helium in the rocks is perfectly consistent with their biblical age of a few thousand years!

It is wildly inconsistent with billions of years. But the fact that such helium is present also indicates that a great deal of radioactive decay has happened; a lot of uranium atoms have decayed into lead, producing the helium. At the current half-life of uranium, this would take billions of years.

How Do We Know the Earth Is 4.6 Billion Years Old?

But if it actually took billions of years, then the helium would have escaped the rocks. The only reasonable explanation that fits all the data is that the half-life of uranium was much smaller in the past.

That is, in the past, uranium transformed into lead much faster than it does today. The RATE team found similar evidence for other forms of radioactive decay. Apparently, during the creation week and possibly during the year of the global flood, radioactive decay rates were much faster than they are today.

Each year a tree adds a layer of wood to its trunk and branches thus creating the annual rings we see when viewing a cross section. Wide rings are produced during wet years and narrow rings during dry seasons. This technique has posed a different problem for creationists, as this dating method does not make use directly of accelerated decay.

By using dendrochronology scientists have dated certain living trees to having ages of around years. This finding showed the current model for carbon dating to be incorrect, so scientists recalibrated their 14 C model based on this tree. Relative dating is a technique that uses the "relative" positions of layers and fossils to assign estimated dates to strata.

Uniformitarian geologists began using the principles of stratigraphy to assign dates to the layers of the geological column fossils back in the late s. Relative dating uses a combination of fossil studies and structural interpretation to draw conclusions about the geological history of an area. Ice cores are obtained by drilling core samples of ice in glaciated regions, such as near the poles. Visible light and dark rings can be found in such cores that are then analyzed to determine the age of the ice.

These layers are presumed to be the result of annual fluctuations in climate, and using this method, uniformitarians purport to document ages of overyears.

Creationists, such as Michael Oardcontend that these laminations are from subannual events, including layering due to dust to be found in a post-flood ice age.

He discusses this theory briefly here. Subannual formation is supported by observations that several such layers of snow and ice can result from the storms within a single winter season.

Any dating method depends on a fixed standard, or else it produces arbitrary dates. Uniformitarian geologists prefer to believe, and claim, that each of their methods uses such a fixed standard. But a careful examination of the so-called "standards" of dating reveals that each of their methods depends on an a priori assumption about the history of the earth.

How Old is that Rock?

By continuing to use such methods, uniformitarians make their own chief assertion, that the earth is billions of years old, untestable. In so doing, they commit the logical fallacies of proof by assertion and circular reasoning. Beyond this, each dating method has problems with the method itself and problems with the interpretation of its results. Some of the "adjustments" that uniformitarians make to the dates that their procedures produce are akin to the detestable practice of "dry-labbing" wherein a dishonest investigator constructs observations out of his own imagination.

The adjustments of carbon dates to make them concordant with other dating methods is a case in point. Many sites get labeled a certain age based on evolutionary bias, but later get redated at much younger dates. A good example of this is the Barberton deposits. It was thought to be the product of a Archean hydrothermal vent, but supposedly it's now from a Cenozoic hydrological system.

Young earth creation scientists believe that the evolutionary geological timescale is in error. It should be noted that catastrophism is increasing being accepted in the field of geology.

The result is that these dating methods only produce old ages for the Earth within the evolutionary theoretical system. Within the creation theoretical system. Using relative and radiometric dating methods, geologists are able to answer the Second, it is possible to determine the numerical age for fossils or earth. While there are numerous experimental methods used to determine geologic ages, the most frequently employed technique is radiometric.

For example, William R. Corliss catalogued numerous anomalies in the old earth uniformatarian geology paradigm. The Northwest Creation Network is a Christian ministry that provides free education and resources in Biblical apologetics.

In dating any object, geologists: Observe the present state of the system. The atomic nucleus that decays is called the parent isotope. The product of the decay is called the daughter isotope.

In the example, 14 C is the parent and 14 N is the daughter. Some minerals in rocks and organic matter e. The abundances of parent and daughter isotopes in a sample can be measured and used to determine their age. This method is known as radiometric dating. Some commonly used dating methods are summarized in Table 1. The rate of decay for many radioactive isotopes has been measured and does not change over time. Thus, each radioactive isotope has been decaying at the same rate since it was formed, ticking along regularly like a clock.

For example, when potassium is incorporated into a mineral that forms when lava cools, there is no argon from previous decay argon, a gas, escapes into the atmosphere while the lava is still molten. When that mineral forms and the rock cools enough that argon can no longer escape, the "radiometric clock" starts. Over time, the radioactive isotope of potassium decays slowly into stable argon, which accumulates in the mineral. The amount of time that it takes for half of the parent isotope to decay into daughter isotopes is called the half-life of an isotope Figure 5b.

When the quantities of the parent and daughter isotopes are equal, one half-life has occurred. If the half life of an isotope is known, the abundance of the parent and daughter isotopes can be measured and the amount of time that has elapsed since the "radiometric clock" started can be calculated.

For example, if the measured abundance of 14 C and 14 N in a bone are equal, one half-life has passed and the bone is 5, years old an amount equal to the half-life of 14 C. If there is three times less 14 C than 14 N in the bone, two half lives have passed and the sample is 11, years old. However, if the bone is 70, years or older the amount of 14 C left in the bone will be too small to measure accurately.

Thus, radiocarbon dating is only useful for measuring things that were formed in the relatively recent geologic past.

Luckily, there are methods, such as the commonly used potassium-argon K-Ar methodthat allows dating of materials that are beyond the limit of radiocarbon dating Table 1. Comparison of commonly used dating methods. Radiation, which is a byproduct of radioactive decay, causes electrons to dislodge from their normal position in atoms and become trapped in imperfections in the crystal structure of the material.

Dating methods like thermoluminescenceoptical stimulating luminescence and electron spin resonancemeasure the accumulation of electrons in these imperfections, or "traps," in the crystal structure of the material.

If the amount of radiation to which an object is exposed remains constant, the amount of electrons trapped in the imperfections in the crystal structure of the material will be proportional to the age of the material.

These methods are applicable to materials that are up to aboutyears old. However, once rocks or fossils become much older than that, all of the "traps" in the crystal structures become full and no more electrons can accumulate, even if they are dislodged. The Earth is like a gigantic magnet. It has a magnetic north and south pole and its magnetic field is everywhere Figure 6a.

Just as the magnetic needle in a compass will point toward magnetic north, small magnetic minerals that occur naturally in rocks point toward magnetic north, approximately parallel to the Earth's magnetic field. Because of this, magnetic minerals in rocks are excellent recorders of the orientation, or polarityof the Earth's magnetic field.

Small magnetic grains in rocks will orient themselves to be parallel to the direction of the magnetic field pointing towards the north pole.

The processes of plate tectonics mean that the Earth is constantly a rock's age often falls to the scientific techniques of radiometric dating, the. “Science has proved that the earth is billion years old. Is radiometric dating a reliable method for estimating the age of something?. Boltwood gave up work on radiometric dating and Rutherford remained mildly curious about the issue of the age of Earth but did helium method until and then ceased.

Black bands indicate times of normal polarity and white bands indicate times of reversed polarity. Through geologic time, the polarity of the Earth's magnetic field has switched, causing reversals in polarity. The Earth's magnetic field is generated by electrical currents that are produced by convection in the Earth's core. During magnetic reversals, there are probably changes in convection in the Earth's core leading to changes in the magnetic field.

The Earth's magnetic field has reversed many times during its history. When the magnetic north pole is close to the geographic north pole as it is todayit is called normal polarity. Reversed polarity is when the magnetic "north" is near the geographic south pole.

Using radiometric dates and measurements of the ancient magnetic polarity in volcanic and sedimentary rocks termed paleomagnetismgeologists have been able to determine precisely when magnetic reversals occurred in the past.

Combined observations of this type have led to the development of the geomagnetic polarity time scale GPTS Figure 6b. The GPTS is divided into periods of normal polarity and reversed polarity. Geologists can measure the paleomagnetism of rocks at a site to reveal its record of ancient magnetic reversals. Every reversal looks the same in the rock record, so other lines of evidence are needed to correlate the site to the GPTS. Information such as index fossils or radiometric dates can be used to correlate a particular paleomagnetic reversal to a known reversal in the GPTS.

Once one reversal has been related to the GPTS, the numerical age of the entire sequence can be determined. Using a variety of methods, geologists are able to determine the age of geological materials to answer the question: "how old is this fossil?

These methods use the principles of stratigraphy to place events recorded in rocks from oldest to youngest. Absolute dating methods determine how much time has passed since rocks formed by measuring the radioactive decay of isotopes or the effects of radiation on the crystal structure of minerals. Paleomagnetism measures the ancient orientation of the Earth's magnetic field to help determine the age of rocks.

Deino, A. Evolutionary Anthropology 6 : Faure, G. Isotopes: Principles and Applications. Third Edition. New York: John Wiley and Sons Gradstein, F. The Geologic Time Scale2-volume set. Waltham, MA: Elsevier Ludwig, K. Geochronology on the paleoanthropological time scale, Evolutionary Anthropology 9, McDougall I.

Tauxe, L. Essentials of paleomagnetism. Characteristics of Crown Primates.

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