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.
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The Archean eon, extending from 3. Because radioactive materials were present in amounts far greater than today, the heat from their decay drove volcanism and other geologic activity at extraordinary rates. Geologists do not agree on whether plate tectonics were active during the Archean eon or whether Earth's crust was even made up of plates at this time.
How reliable is geologic dating?
However, smaller land masses were developing and being destroyed and rocks were forming at much higher temperatures than are possible today. The atmosphere was radically different as well, containing very little oxygen. Certain kinds of iron ores formed that would not have been possible had oxygen been present in the atmosphere. Most modern life forms could not have survived in the oxygen-poor atmosphere of the Archean eon.
Despite the lack of oxygen, the first kinds of life arose in the Archean: Many different kinds of fossilized stromatolites have been found in different rock formations around the world, giving geologists a great deal of information about the Archean eon. They show that different kinds of bacteria lived together in an ecosystem, that some bacteria used photosynthesis to generate energy from the sun while others relied on different sources, and that areas of both shallow and deep water were present.
Although the fossil evidence from the Archean is limited, all the life forms discovered so far have been single-celled prokaryotes that lack a nucleus. The Archean was followed by the Proterozoic, occurring between 2. During this eon life began to transform into types that we recognize today, changing Earth along with it. Shallow seas formed and the atmosphere began to change as well. During the Paleoproterozoic era the earliest part of the Proterozoic eon an event known as the oxygen catastrophe occurred: Since the Archean eon, early bacteria had been excreting oxygen as a waste product.
Initially, most of the oxygen was consumed in the oxidation of minerals and metals such as iron. As the amount of unoxidized iron began to decrease, the amount of oxygen in the atmosphere increased. This poisoned some types of anaerobic Archean bacteria, but spurred others to use oxygen in their metabolism, a much more efficient way of processing energy.
Aerobic organisms became dominant in the Proterozoic eon. The Mesoproterozoic era the middle part of the Proterozoic eon saw the development of eukaryotes, single-celled organisms with a nucleus. During the end of the Neoproterozoic era the most recent part of the eon , in a division known as the Ediacaran period, the earliest complex multicellular organisms appeared. These soft-bodied creatures appear to have lived on the bottom of shallow seas, not unlike modern corals or sponges.
They were diverse in size, structural complexity, shape, and symmetry. The Ediacaran period is the most recently recognized of all the eons, eras, and periods, named for the Ediacara area in Australia, where many of the fossils have been found. Alongside the rapidly changing life forms of the Proterozoic eon, significant geological processes were occurring. The supercontinent called Rodinia formed at the end of the Stenian period in the Mesoproterozoic. The first ice ages occurred during the Proterozoic era. The end of the Proterozoic is marked by a dramatic event in the fossil record known as the Cambrian explosion.
At this time, a remarkable increase in the numbers and types of species is seen, as well as the first hard-bodied animals, i. During this time, life evolved from the simplest sponges, jellyfish, and worms to include almost everything we can think of that is alive today. Geological periods during the Phanerozoic are divided into smaller epochs based on changes in the kinds of life that appear in the fossil record. The larger number of fossilized species present and the relatively short period of time since their deposit allow this more precise dating.
The largest divisions of the Phanerozoic eon are the Paleozoic, Mesozoic, and Cenozoic eras. Each lasted for millions of years and each is broadly characterized by the degree of development that the life within it has undergone. The Paleozoic is divided into the Cambrian, Ordovician, Silurian, Devonian, Carboniferous which is sometimes divided into the Mississippian and Pennsylvanian eras and Permian periods. Each of these is further divided into several epochs, some named for places where their major characteristics were discovered, others simply divided into early, middle, and late epochs.
During the Paleozoic era , insects, plants, the first vertebrate animals, amphibians, reptiles, fish, sharks, and corals all appeared. Often, it is the changes in the kinds of animals and plants that are used to decide boundaries between the different periods.
Despite the emphasis on life in describing the various ages of the Paleozoic, geologic processes were still. Supercontinents formed and broke apart, several ice ages advanced and retreated, temperatures fluctuated, and sea levels rose and fell. These diverse processes influenced the many changes in life that are recorded in the fossils of the era—coal deposits in Europe laid down during the Carboniferous period are one of its more famous features.
At the end of the Paleozoic era , a disastrous event known as the Permian-Triassic extinction led to the destruction of almost all Paleozoic species.
Though there have been efforts to link this extinction to a meteorite impact, no convincing evidence of a large enough collision during this time period has been found. Dinosaurs appeared during the Mesozoic era. The names of the periods in the Mesozoic era may sound familiar: Triassic, Jurassic, and Cretaceous. During this million-year era, all the familiar dinosaurs such as triceratops, tyrannosaurus, stegosaurus, diplodocus, and apatosaurus flourished at different times.
Some modern animals have ancestors that first appeared during the Mesozoic era, including birds, crocodiles, and mammals. Plants continued to develop, and the first flowering plants appeared. The end of the Mesozoic era can be seen clearly in some rock layers. Known as the K-T Cretaceous-Tertiary boundary, this dark line of sediment is rich in the element iridium.
Another massive extinction of species occurred at this time, possibly because of one or more meteorite impacts along with a period of intense volcanic activity. This would have decreased the amount of sunlight reaching Earth's surface, killing plants and, eventually, animals. Not all geologists and paleontologists are convinced that the K-T extinction was a catastrophic event; some argue that it occurred over a few million years after slower climate changes. The Cenozoic era , the current era of geologic time, is divided into the Paleogene and Neogene periods, and further into the Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene epochs.
During the Cenozoic, the supercontinent of Gondwana broke apart, and the continents reached their current positions. Different cations move throughout the environment at different rates, so the ratio of different cations to each other changes over time. By calibrating these ratios with dates obtained from rocks from a similar microenvironment, a minimum age for the varnish can be determined. This technique can only be applied to rocks from desert areas, where the varnish is most stable.
Although cation-ratio dating has been widely used, recent studies suggest it has potential errors. Many of the dates obtained with this method are inaccurate due to improper chemical analyses. In addition, the varnish may not actually be stable over long periods of time. Thermoluminescence dating is very useful for determining the age of pottery. Electrons from quartz and other minerals in the pottery clay are bumped out of their normal positions ground state when the clay is exposed to radiation.
This radiation may come from radioactive substances such as uranium,. The longer the radiation exposure, the more electrons get bumped into an excited state.
With more electrons in an excited state, more light is emitted upon heating. The process of displacing electrons begins again after the object cools. Scientists can determine how many years have passed since a ceramic was fired by heating it in the laboratory and measuring how much light is given off.
Thermoluminescence dating has the advantage of covering the time interval between radiocarbon and potassium-argon dating , or 40, — , years. In addition, it can be used to date materials that cannot be dated with these other two methods. Optically stimulated luminescence OSL has only been used since It is very similar to thermoluminescence dating, both of which are considered "clock setting" techniques. Minerals found in sediments are sensitive to light. Electrons found in the sediment grains leave the ground state when exposed to light, called recombination. To determine the age of sediment, scientists expose grains to a known amount of light and compare these grains with the unknown sediment.
This technique can be used to determine the age of unheated sediments less than , years old. A disadvantage to this technique is that in order to get accurate results, the sediment to be tested cannot be exposed to light which would reset the "clock" , making sampling difficult.
The absolute dating method utilizing tree ring growth is known as dendrochronology. It is based on the fact that trees produce one growth ring each year. The rings form a distinctive pattern, which is the same for all members in a given species and geographical area. The patterns from trees of different ages including ancient wood are overlapped, forming a master pattern that can be used to date timbers thousands of years old with a resolution of one year. Timbers can be used to date buildings and archaeological sites.
In addition, tree rings are used to date changes in the climate such as sudden cool or dry periods. Dendrochronology has a range of one to 10, years or more. As previously mentioned, radioactive decay refers to the process in which a radioactive form of an element is converted into a decay product at a regular rate. Radioactive decay dating is not a single method of absolute dating but instead a group of related methods for absolute dating of samples. Potassium-argon dating relies on the fact that when volcanic rocks are heated to extremely high temperatures, they release any argon gas trapped in them.
As the rocks cool, argon 40 Ar begins to accumulate. Argon is formed in the rocks by the radioactive decay of potassium 40 K. The amount of 40 Ar formed is proportional to the decay rate half-life of 40 K, which is 1. In other words, it takes 1. This method is generally only applicable to rocks greater than three million years old, although with sensitive instruments, rocks several hundred thousand years old may be dated.
The reason such old material is required is that it takes a very long time to accumulate enough 40 Ar to be measured accurately. Potassium-argon dating has been used to date volcanic layers above and below fossils and artifacts in east Africa. Radiocarbon dating is used to date charcoal, wood, and other biological materials. The range of conventional radiocarbon dating is 30, — 40, years, but with sensitive instrumentation, this range can be extended to 70, years. Radiocarbon 14 C is a radioactive form of the element carbon.
It decays spontaneously into nitrogen 14 N. Plants get most of their carbon from the air in the form of carbon dioxide , and animals get most of their carbon from plants or from animals that eat plants. Relative to their atmospheric proportions, atoms of 14 C and of a non-radioactive form of carbon, 12 C, are equally likely to be incorporated into living organisms. When the organism dies, however, its body stops incorporating new carbon. The ratio will then begin to change as the 14 C in the dead organism decays into 14 N.
Age of the Earth
The rate at which this process occurs is called the half-life. This is the time required for half of the 14 C to decay into 14 N. The half-life of 14 C is 5, years. This allows them to determine how much 14 C has formed since the death of the organism. One of the most familiar applications of radioactive dating is determining the age of fossilized remains, such as dinosaur bones. Radioactive dating is also used to authenticate the age of rare archaeological artifacts.
Because items such as paper documents and cotton garments are produced from plants, they can be dated using radiocarbon dating. Without radioactive dating , a clever forgery might be indistinguishable from a real artifact. There are some limitations, however, to the use of this technique. Samples that were heated or irradiated at some time may yield by radioactive dating an age less than the true age of the object.
Because of this limitation, other dating techniques are often used along with radioactive dating to ensure accuracy. Uranium series dating techniques rely on the fact that radioactive uranium and thorium isotopes decay into a series of unstable, radioactive "daughter" isotopes; this process continues until a stable non-radioactive lead isotope is formed. The daughters have relatively short half-lives ranging from a few hundred thousand years down to only a few years.
The "parent" isotopes have half-lives of several billion years. This provides a dating range for the different uranium series of a few thousand years to , years. Uranium series have been used to date uranium-rich rocks, deep-sea sediments, shells, bones, and teeth, and to calculate the ages of ancient lakebeds. The two types of uranium series dating techniques are daughter deficiency methods and daughter excess methods. In daughter deficiency situations, the parent radioisotope is initially deposited by itself, without its daughter the isotope into which it decays present.
Through time, the parent decays to the daughter until the two are in equilibrium equal amounts of each. The age of the deposit may be determined by measuring how much of the daughter has formed, providing that neither isotope has entered or exited the deposit after its initial formation.
Living mollusks and corals will only take up dissolved compounds such as isotopes of uranium, so they will contain no protactinium, which is insoluble. Protactinium begins to accumulate via the decay of U after the organism dies. Scientists can determine the age of the sample by measuring how much Pa is present and calculating how long it would have taken that amount to form.
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- Earth Science: Geologic Ages and Dating Techniques;
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In the case of daughter excess, a larger amount of the daughter is initially deposited than the parent. Non-uranium daughters such as protactinium and thorium are insoluble, and precipitate out on the bottoms of bodies of water, forming daughter excesses in these sediments. Over time, the excess daughter disappears as it is converted back into the parent, and by measuring the extent to which this has occurred, scientists can date the sample.
If the radioactive daughter is an isotope of uranium, it will dissolve in water, but to a different extent than the parent; the two are said to have different solubilities. For example, U dissolves more readily in water than its parent, U, so lakes and oceans contain an excess of this daughter isotope. Some volcanic minerals and glasses, such as obsidian , contain uranium U. Over time, these substances become "scratched. When an atom of U splits, two "daughter" atoms rocket away from each other, leaving in their wake tracks in the material in which they are embedded.
The rate at which this process occurs is proportional to the decay rate of U. The decay rate is measured in terms of the half-life of the element, or the time it takes for half of the element to split into its daughter atoms. The half-life of U is 4. When the mineral or glass is heated, the tracks are erased in much the same way cut marks fade away from hard candy that is heated. This process sets the fission track clock to zero, and the number of tracks that then form are a measure of the amount of time that has passed since the heating event.
Scientists are able to count the tracks in the sample with the aid of a powerful microscope. The sample must contain enough U to create enough tracks to be counted, but not contain too much of the isotope, or there will be a jumble of tracks that cannot be distinguished for counting.
One of the advantages of fission track dating is that it has an enormous dating range. Objects heated only a few decades ago may be dated if they contain relatively high levels of U; conversely, some meteorites have been dated to over a billion years old with this method. Although certain dating techniques are accurate only within certain age ranges, whenever possible, scientists attempt to use multiple methods to date specimens. Correlation of dates via different dating methods provides a highest degree of confidence in dating. See also Evolution, evidence of; Fossil record; Fossils and fossilization; Geologic time; Historical geology.
Cite this article Pick a style below, and copy the text for your bibliography. Retrieved January 17, from Encyclopedia. Then, copy and paste the text into your bibliography or works cited list. Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia. Movies and television have presented a romantic vision of archaeology as adventure in far-away and exotic locations. A more realistic picture might show researchers digging in smelly mud for hours under the hot sun while battling relentless mosquitoes.
- The Age of the Earth.
- Strengths and weaknesses of radiometric and other dating methods.
- Non-radiometric Dating.
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This type of archaeological research produces hundreds of small plastic bags containing pottery shards, animal bones, bits of worked stone, and other fragments. These findings must be classified, which requires more hours of tedious work in a stuffy tent. At its best, archaeology involves a studious examination of the past with the goal of learning important information about the culture and customs of ancient or not so ancient peoples. Much archaeology in the early twenty-first century investigates the recent past, a sub-branch called "historical archaeology.
Archaeology is the study of the material remains of past human cultures. It is distinguished from other forms of inquiry by its method of study, excavation. Most archaeologists call this "digging. That sort of unscientific digging destroys the archaeological information. Archaeological excavation requires the removal of material layer by layer to expose artifacts in place. The removed material is carefully sifted to find small artifacts , tiny animal bones, and other remains.
Archaeologists even examine the soil in various layers for microscopic material, such as pollen. Excavations, in combination with surveys, may yield maps of a ruin or collections of artifacts. Time is important to archaeologists. There is rarely enough time to complete the work, but of even greater interest is the time that has passed since the artifact was created. An important part of archaeology is the examination of how cultures change over time. It is therefore essential that the archaeologist is able to establish the age of the artifacts or other material remains and arrange them in a chronological sequence.
The archaeologist must be able to distinguish between objects that were made at the same time and objects that were made at different times. When objects that were made at different times are excavated, the archaeologist must be able to arrange them in a sequence from the oldest to the most recent.
Before scientific dating techniques such as dendrochronology and radiocarbon dating were introduced to archaeology, the discipline was dominated by extensive discussions of the chronological sequence of events. Most of those questions have now been settled and archaeologists have moved on to other issues. Scientific dating techniques have had a huge impact on archaeology. Archaeologists use many different techniques to determine the age of an object.
Usually, several different techniques are applied to the same object. Relative dating arranges artifacts in a chronological sequence from oldest to most recent without reference to the actual date. For example, by studying the decorations used on pottery, the types of materials used in the pottery, and the types and shapes of pots, it is often possible to arrange them into a sequence without knowing the actual date.
In absolute dating , the age of an object is determined by some chemical or physical process without reference to a chronology. The most common and widely used relative dating technique is stratigraphy. The principle of superposition borrowed from geology states that higher layers must be deposited on top of lower layers. Thus, higher layers are more recent than lower layers. This only applies to undisturbed deposits. Rodent burrows, root action, and human activity can mix layers in a process known as bioturbation.
However, the archaeologist can detect bioturbation and allow for its effects. Discrete layers of occupation can often be determined. For example, Hisarlik, which is a hill in Turkey , is thought by some archaeologists to be the site of the ancient city of Troy. However, Hisarlik was occupied by many different cultures at various times both before and after the time of Troy, and each culture built on top of the ruins of the previous culture, often after violent conquest. Consequently, the layers in this famous archaeological site represent many different cultures.
An early excavator of Hisarlik, Heinrich Schleimann, inadvertently dug through the Troy layer into an earlier occupation and mistakenly assigned the gold artifacts he found there to Troy. Other sites have been continuously occupied by the same culture for a long time and the different layers represent gradual changes. In both cases, stratigraphy will apply. A chronology based on stratigraphy often can be correlated to layers in other nearby sites. For example, a particular type or pattern of pottery may occur in only one layer in an excavation.
If the same pottery type is found in another excavation nearby, it is safe to assume that the layers are the same age. Archaeologists rarely make these determinations on the basis of a single example. Usually, a set of related artifacts is used to determine the age of a layer. Seriation simply means ordering. This technique was developed by the inventor of modern archaeology, Sir William Matthew Flinders Petrie.
Seriation is based on the assumption that cultural characteristics change over time. For example, consider how automobiles have changed in the last 50 years a relatively short time in archaeology. Automobile manufacturers frequently introduce new styles about every year, so archaeologists thousands of years from now will have no difficulty identifying the precise date of a layer if the layer contains automobile parts. Cultural characteristics tend to show a particular pattern over time. The characteristic is introduced into the culture for example, using a certain type of projectile point for hunting or wearing low-riding jeans , becomes progressively more popular, then gradually wanes in popularity.
The method of seriation uses this distinctive pattern to arrange archaeological materials into a sequence. However, seriation only works when variations in a cultural characteristic are due to rapid and significant change over time. It also works best when a characteristic is widely shared among many different members of a group. Even then, it can only be applied to a small geographic area, because there is also geographic variation in cultural characteristics.
For example, 50 years ago American automobiles changed every year while the Volkswagen Beetle hardly changed at all from year to year. Cross dating is also based on stratigraphy. It uses the principle that different archaeological sites will show a similar collection of artifacts in layers of the same age. Sir Flinders Petrie used this method to establish the time sequence of artifacts in Egyptian cemeteries by identifying which burials contained Greek pottery vessels. This idea has been rebutted by those who claim there is no known scientific mechanism to produce such a change, see for example Tim-Thompson: Others disagree and say that studies in theoretical physics suggest accelerated nuclear decay can occur e.
Uniformitarianism is also challenged if we invoke the concept of a world-wide flood for which there is much evidence. Vardiman et al claim that this would result in unreliable radioisotopic dating. They conclude from their research that:. Let's take a deeper look into the theory of accelerated nuclear decay. Classical OE dating radiometric dating is based upon the spontaneous breakdown or decay of atomic nuclei, where a radioactive parent atom decays to a stable daughter atom.
The clash between OE dating millions or billions of years and YE dating thousands of years centres on the decay constant K. As discussed, OE dating rests on the evolutionary concept of uniformitarianism and an assumed constant decay rate for all time. But this is not necessarily so. The Decreasing Speed of Light: In , Albrecht and Magueijo proposed a reduction in 'c' over time as a solution to cosmological puzzles.
For example, theories in which light is traveling faster in the early periods of the existence of the Universe have been recognised as an alternative to the 'big bang' inflation scenario, see Pedram and Jalalzadeh. So, rather than 'c' being constant with time, it has been proposed that the product 'hc' where here 'h' is Planks Constant and 'c' is the speed of light in a vacuum should be considered constant, see Setterfield.
Even in recent times, hundreds of measurements of 'c' since show a small but statistically significant decrease i. See also speed measurments and discussion. The Effect of Changes in 'c': As just noted, some in the scientific community now claim that the radioactive decay 'constant' K can be changed i. In particular, Setterfield has shown that K is strongly related to 'c'. So if the speed of light slows down, then the radioactive decay rate also slows down, link.
It is argued like this:. It follows that radioactive decay rates were much higher in the past. In other words, when 'c' was higher, atomic clocks ticked more rapidly and 'atomic time' ran fast. So standard radiometric dating must be corrected for this early accelerated decay rate , reducing millions of years to thousands! The current scientific argument for an old earth is popular especially in the media and education whilst the concept of a young earth as held by Creationism is given low profile and so seems relatively weak.
For example, non-radiometric dating techniques using ice cores do indeed appear to date the earth well in excess of , years. But there are several factors in favour of a young earth. These are largely ignored by mainstream science but could be the key to the massive discrepancy when it comes to dating the earth. At the Fall of man the whole of creation, including the earth, was suddenly subjected to corruption or decay Rom 8.
Man suddenly had a limited lifespan Gen 2. Also, at the Flood there were catastrophic geological changes, see for example geological evidence for the flood and scientific evidence. Some see these physical events as being related to changes in physical laws e. In short, the earth's order is deteriorating with time, and "the earth is wearing out like a garment" Isa This concept seems to be supported by theoretical physics, which suggests that a decrease in the speed of light, c, see Is the Velocity of Light Constant in Time?
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Physical changes are also suggested from the biblical accounts of man living to over years prior to the Flood Gen 5 , followed by an exponential decrease in age after the Flood. Some suggest this could be from a significant increase in radioisotopes in the atmosphere after the Flood. Could these biblical events and the associated physical changes have caused accelerated radiometric decay , and by implication destroy uniformitarianism, the bedrock of radiometric dating?
If so, standard radiometric dating must be corrected for an early accelerated decay rate, reducing millions of years to thousands! These biblically-implied abrupt physical changes in the earth are largely ignored in radiometric dating, which may be the source of the OE and YE discrepancy. These physical changes also affect the assumptions in radiocarbon dating and ice core dating.
For more detail see A Young Earth Model. For many Christians the jury is still out. The OE theory and associated evolutionary theory is well supported by high profile scientific bodies such as The Royal Society , and by the media. But there are serious dissenting scientific voices on evolutionary theory , and conventional earth dating techniques , and a growing Creation Science community make a good case for a Young Earth. Various dating clocks, such as the earth's decaying magnetic field and population growth suggest a young earth, and the classical radiometric dating assumption of Uniformitarianism has to be questioned given possible change in physical constants.
Also, theologically it seems difficult to accept OE creationism theistic evolution and dismiss YE creationism when the Bible is read literally and when Jesus Himself implied a young earth see biblical earth dating. The basic question seems to be "where is one's starting point? For all Christians this should be:. Variation in compactified dimensions could affect coupling constants Consequent variation in coupling constants could cause accelerated decay Changes in potential well depth change the alpha-particle wave function Changes in the alpha-particle wave function change decay half-lives.
Physical changes to the earth at the Fall of Man Physical changes to the earth during the Flood.