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Geologists count back more than 4 billion years to the oldest Earth materials. Have you ever tried to count to a million? Counting once per second easy at the start, but tough when you reach the hundred-thousand mark , 24 hours per day, seven days per week no weekends off , it would take you 11 days, 14 hours to count to one million! There are a thousand millions in a billion, so counting to a billion would take you approximately 32 years. Taking this one step further, it is not humanly possible to count to 4. To help comprehend the length of geologic time, some analogies are provided below. Select an analogy:.

The atomic number is reduced by one and mass number remains the same. An example of an element that decays by electron capture is potassium 40 K. Radioactive 40 K makes up a tiny percentage 0. Below is a table of some of the more commonly-used radioactive dating isotopes and their half-lives.

Some common isotopes used for radioisotopic dating. For a given a sample of rock, how is the dating procedure carried out? The parent and daughter isotopes are separated out of the mineral using chemical extraction. In the case of uranium, U and U isotopes are separated out together, as are the Pb and Pb with an instrument called a mass spectrometer. Graph of number of half-lives vs.

This can be further calculated for a series of half-lives as shown in the table. The table does not show more than 10 half-lives because after about 10 half-lives, the amount of remaining parent is so small it becomes too difficult to accurately measure via chemical analysis.

Modern applications of this method have achieved remarkable accuracies of plus or minus two million years in 2. The existence of these two clocks in the same sample gives a cross-check between the two. Ratio of parent to daughter in terms of half-life.

Schematic of carbon going through a mass spectrometer. Another radioisotopic dating method involves carbon and is useful for dating archaeologically important samples containing organic substances like wood or bone. Radiocarbon datingalso called carbon dating, uses the unstable isotope carbon 14 C and the stable isotope carbon 12 C. Carbon is constantly being created in the atmosphere by the interaction of cosmic particles with atmospheric nitrogen 14 N.

Cosmic particles such as neutrons strike the nitrogen nucleus, kicking out a proton but leaving the neutron in the nucleus. The collision reduces the atomic number by one, changing it from seven to six, changing the nitrogen into carbon with the same mass number of The 14 C quickly bond Two or more atoms or ions that are connected chemically.

However, when it dies, the radiocarbon clock starts ticking as the 14 C decays back to 14 N by beta decaywhich has a half-life of 5, years. The radiocarbon dating technique is thus useful for 57, years or so, about 10 half-lives back.

Radiocarbon dating relies on daughter-to-parent ratios derived from a known quantity of parent 14 C. Early applications of carbon dating assumed the production and concentration of 14 C in the atmosphere remained fairly constant for the last 50, years. However, it is now known that the amount of parent 14 C levels in the atmosphere. Comparisons of carbon ages with tree-ring data and other data for known events have allowed reliable calibration of the radiocarbon dating method.

Taking into account carbon baseline levels must be calibrated against other reliable dating methods, carbon dating has been shown to be a reliable method for dating archaeological specimens and very recent geologic events.

The work of Hutton and other scientists gained attention after the Renaissance see Chapter 1spurring exploration into the idea of an ancient Earth. In the late 19 th century William Thompson, a. Lord Kelvin, applied his knowledge of physics to develop the assumption that the Earth started as a hot molten sphere.

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 date past events, processes, formations, and fossil organisms, geologists employ a variety of techniques. A Geologic Time Scale Relative dating is the process of determining if one rock or geologic event is older or younger than another, without knowing their specific ages-i.e., how many years ago the object was formed. The principles of relative time are simple, even obvious now. Aug 11,   Relative dating is the process of determining if one rock or geologic event is older or younger than another, without knowing their specific ages-i.e., how many years ago the object was formed. The principles of relative time are simple, even obvious now, but were not generally accepted by scholars until the scientific revolution of the 17th.

He estimated the Earth is 98 million years old, but because of uncertainties in his calculations stated the age as a range of between 20 and million years. This animation illustrates how Kelvin calculated this range and why his numbers were so far off, which has to do with unequal heat transfer within the Earth. Patterson analyzed meteorite samples for uranium and lead using a mass spectrometer. The current estimate for the age of the Earth is 4.

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It is remarkable that Patterson, who was still a graduate student at the University of Chicago, came up with a result that has been little altered in over 60 years, even as technology has improved dating methods.

Radioactive isotopes of elements that are common in mineral crystals are useful for radioisotopic dating.

Zircon is resistant to weathering which makes it useful for dating geological events in ancient rocks. During metamorphic events, zircon crystals may form multiple crystal layers, with each layer recording the isotopic age of an event, thus tracing the progress of the several metamorphic events.

Geologists have used zircon grains to do some amazing studies that illustrate how scientific conclusions can change with technological advancements. Zircon crystals from Western Australia that formed when the crust first differentiated from the mantle 4.

The zircon grains were incorporated into metasedimentary host rocks, sedimentary rocks showing signs of having undergone partial metamorphism. The host rocks were not very old but the embedded zircon grains were created 4.

From other properties of the zircon crystals, researchers concluded that not only were continental rocks exposed above sea level, but also that conditions on the early Earth were cool enough for liquid water to exist on the surface.

The presence of liquid water allowed the processes of weathering and erosion to take place. Researchers at UCLA studied 4. Igneous rocks best suited for radioisotopic dating because their primary minerals provide dates of crystallization from magma. Detrital sedimentary rocks are less useful because they are made of minerals derived from multiple parent sources with potentially many dates.

However, scientists can use igneous events to date sedimentary sequences. For example, if sedimentary strata are between a lava Liquid rock on the surface of the Earth.

Another example would be a 65 million year old volcanic dike A narrow igneous intrusion that cuts through existing rock, not along bedding planes. This provides an upper limit age on the sedimentary strataso this strata would be older than 65 million years.

Primary sedimentary minerals containing radioactive isotopes like 40 K, has provided dates for important geologic events. Thermoluminescence, a type of luminescence dating Luminescence aka Thermoluminescence : Radioisotopic dating is not the only way scientists determine numeric ages. Luminescence dating measures the time elapsed since some silicate mineralssuch as coarse- sediments of silicate mineralswere last exposed to light or heat at the surface of Earth.

All buried sediments are exposed to radiation from normal background radiation from the decay process described above. Some of these electrons get trapped in the crystal lattice of silicate minerals like quartz. When exposed at the surface, ultraviolet radiation and heat from the Sun releases these electrons, but when the minerals are buried just a few inches below the surface, the electrons get trapped again.

Samples of coarse sediments collected just a few feet below the surface are analyzed by stimulating them with light in a lab. This stimulation releases the trapped electrons as a photon of light which is called luminescence. The amount luminescence released indicates how long the sediment has been buried. Luminescence dating is only useful for dating sediments young sediment that are less than 1 million years old. In Utah, luminescence dating is used to determine when coarse-grained sediment layers were buried near a fault.

This is one technique used to determine the recurrence interval of large earthquakes on faults like the Wasatch Fault that primarily cut coarse-grained material and lack buried organic soil A type of non-eroded sediment mixed with organic matter, used by plants. Many essential elements for life, like nitrogen, are delivered to organisms via the soil. Apatite from Mexico.

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Fission Track: Fission track dating relies on damage to the crystal lattice produced when unstable U decays to the daughter product Th and releases an alpha particle. These two decay products move in opposite directions from each other through the crystal lattice leaving a visible track of damage. This is common in uranium-bearing mineral grains such as apatite.

The tracks are large and can be visually counted under an optical microscope. The number of tracks correspond to the age of the grains.

Fission track dating has also been used as a second clock to confirm dates obtained by other methods. They may be actual remains of body parts rareimpressions of soft body parts, cast Material filling in a cavity left by a organism that has dissolved away. The body parts of living organisms range from the hard bones and shells of animals, soft cellulose of plants, soft bodies of jellyfish, down to single cells of bacteria and algae. Which body parts can be preserved?

The best environment for preservation is the ocean, yet marine processes can dissolve hard parts and scavenging can reduce or eliminate remains. Thus, even under ideal conditions in the ocean, the likelihood of preservation is quite limited.

Relative dating geologic time

For terrestrial life, the possibility of remains being buried and preserved is even more limited. In other words, the fossil record is incomplete and records only a small percentage of life that existed. Although incomplete, fossil records are used for stratigraphic correlationusing the Principle of Faunal Successionand provide a method used for establishing the age of a formation on the Geologic Time Scale. Trilobites had a hard exoskeleton and are often preserved by permineralization.

Remnants or impressions of hard parts, such as a marine clam shell or dinosaur bone, are the most common types of fossils. The original material has almost always been replaced with new minerals that preserve much of the shape of the original shell, bone, or cell. The common types of fossil preservation are actual preservationpermineralizationmold Organic material making a preserved impression in a rock.

Oct 02,   Relative Dating (Steno's Laws): Long before geologists tried to quantify the age of the Earth they developed techniques to determine which geologic events preceded another, what are termed "relative age" relationships. These techniques were first articulated by Nicolas Steno, a Dane living in the Medici court of Italy in the 17th C. Relative dating is the science of determining the relative order of past events (i.e., the age of an object in comparison to another), without necessarily determining their absolute age (i.e. estimated age). In geology, rock or superficial deposits, fossils and lithologies can be used to correlate one stratigraphic column with another. Prior to the discovery of radiometric dating in .

Actual preservation is a rare form of fossilization where the original materials or hard parts of the organism are preserved. Preservation of soft-tissue is very rare since these organic materials easily disappear because of bacterial decay. Examples of actual preservation are unaltered biological materials like insects in amber or original minerals like mother-of-pearl on the interior of a shell. Another example is mammoth skin and hair preserved in post- glacial deposits in the Arctic regions.

Rare mummification has left fragments of soft tissue, skin, and sometimes even blood vessels of dinosaurs, from which proteins have been isolated and evidence for DNA fragments have been discovered. Mosquito preserved in amber. Permineralization in petrified wood. The shape of this cavity is an mold Organic material making a preserved impression in a rock. If the mold Organic material making a preserved impression in a rock.

Sometimes internal cavities of organisms, such internal cast Material filling in a cavity left by a organism that has dissolved away. If the chemistry is right, and burial is rapid, mineral nodules form around soft structures preserving the three-dimensional detail. This is called authigenic mineralization.

Carbonized leaf. Trace fossils are indirect evidence left behind by an organism, such as burrows and footprints, as it lived its life. Ichnology is specifically the study of prehistoric animal tracks. Dinosaur tracks testify to their presence and movement over an area, and even provide information about their size, gait, speed, and behavior.

Burrows dug by tunneling organisms tell of their presence and mode of life. Foot prints of the early crocodile Chirotherium. Evolution has created a variety of ancient fossils that are important to stratigraphic correlation.

The British naturalist Charles Darwin recognized that life forms evolve into progeny life forms.

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He proposed natural selection -which operated on organisms living under environmental conditions that posed challenges to survival-was the mechanism driving the process of evolution forward. The basic classification unit of life is the species : a population of organisms that exhibit shared characteristics and are capable of reproducing fertile offspring. For a species to survive, each individual within a particular population is faced with challenges posed by the environment and must survive them long enough to reproduce.

Within the natural variations present in the population, there may be individuals possessing characteristics that give them some advantage in facing the environmental challenges. These individuals are more likely to reproduce and pass these favored characteristics on to successive generations. If sufficient individuals in a population fail to surmount the challenges of the environment and the population cannot produce enough viable offspring, the species becomes extinct.

Between the years of an James Hutton and William Smith advanced the concept of geologic time and strengthened the belief in an ancient world. Hutton, a Scottish geologist, first proposed formally the fundamental principle used to classify rocks according to their relative . Dating Rocks Two major categories of geologic dating techniques exist: relative dating and absolute age determinations. Relative dating determines the order in which a sequence of geologic events (e.g., volcanic eruptions, mountain building, sea-level rise, and deposition of sedimentary strata) occurred, but not how long ago the events happened. Jul 31,   The geologic time scale began to take shape in the s. Geologists first used relative age dating principles to chart the chronological order of rocks around the world. It wasn't until the advent of radiometric age dating techniques in the middle s that reliable numerical dates could be assigned to the previously named geologic time.

The average lifespan of a species in the fossil record is around a million years. That life still exists on Earth shows the role and importance of evolution as a natural process in meeting the continual challenges posed by our dynamic Earth.

If the inheritance of certain distinctive characteristics is sufficiently favored over time, populations may become genetically isolated from one another, eventually resulting in the evolution of separate species.

This genetic isolation may also be caused by a geographic barrier, such as an island surrounded by ocean. Evolution is well beyond the hypothesis stage and is a well-established theory of modern science.

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Variation within populations occurs by the natural mixing of genes through sexual reproduction or from naturally occurring mutations. While some species in the fossil record show little morphological change over time, others show gradual or punctuated changes, within which intermediate forms can be seen. Image showing fossils that connect the continents of Gondwana the southern continents of Pangea. Wegener used correlation to help develop the idea of continental drift.

Correlation is the process of establishing which sedimentary strata are of the same age but geographically separate. Correlation can be determined by using magnetic polarity reversals Chapter 2rock types, unique rock sequences, or index fossils. There are four main types of correlation : stratigraphiclithostratigraphic, chronostratigraphic, and biostratigraphic. Stratigraphic correlation is the process of establishing which sedimentary strata are the same age at distant geographical areas by means of their stratigraphic relationship.

Geologists construct geologic histories of areas by mapping and making stratigraphic columns-a detailed description of the strata from bottom to top. Based on the stratigraphic relationship, the Wingate and Moenave Formations correlate. These two formations have unique names because their composition and outcrop pattern is slightly different. Other strata in the Colorado Plateau and their sequence can be recognized and correlated over thousands of square miles.

Lithos is Greek for stone and -logy comes from the Greek word for doctrine or science. Lithostratigraphic correlation can be used to correlate whole formations long distances or can be used to correlate smaller strata within formations to trace their extent and regional depositional environments.

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Stevens Arch in the Navajo Sandstone at Coyote Gulch some miles away from Zion National Park For example, the Navajo Sandstonewhich makes up the prominent walls of Zion National Park, is the same Navajo Sandstone in Canyonlands because the lithology of the two are identical even though they are hundreds of miles apart.

Extensions of the same Navajo Sandstone formation are found miles away in other parts of southern Utah, including Capitol reef A topographic high found away from the beach in deeper water, but still on the continental shelf. Typically, these are formed in tropical areas by organisms such as corals. Further, this same formation is the called the Aztec Sandstone in Nevada and Nugget Sandstone near Salt Lake City because they are lithologically distinct enough to warrant new names.

Chronostratigraphic correlation matches rocks of the same age, even though they are made of different lithologies. Different lithologies of sedimentary rocks can form at the same time at different geographic locations because depositional environments vary geographically. For example, at any one time in a marine setting there could be this sequence of depositional environments from beach to deep marine : beach, near shore area, shallow marine lagoonreef A topographic high found away from the beach in deeper water, but still on the continental shelf.

Each depositional environment will have a unique sedimentary rock formation. On the figure of the Permian Capitan reef A topographic high found away from the beach in deeper water, but still on the continental shelf.

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All three of these unique lithologies were forming at the same time in Permian along this red timeline. Biostratigraphic correlation uses index fossils to determine strata ages. Index fossils represent assemblages or groups of organisms that were uniquely present during specific intervals of geologic time.

Assemblages is referring a group of fossils. Fossils allow geologists to assign a formation to an absolute date range, such as the Jurassic Period to million years agorather than a relative time scale. In fact, most of the geologic time ranges are mapped to fossil assemblages.

The most useful index fossils come from lifeforms that were geographically widespread and had a species lifespan that was limited to a narrow time interval.

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In other words, index fossils can be found in many places around the world, but only during a narrow time frame. Some of the best fossils for biostratigraphic correlation are microfossilsmost of which came from single-celled organisms.

As with microscopic organisms today, they were widely distributed across many environments throughout the world. Some of these microscopic organisms had hard parts, such as exoskeletons or outer shells, making them better candidates for preservation. Foraminifera, single celled organisms with calcareous shells, are an example of an especially useful index fossil for the Cretaceous Period and Cenozoic era The second largest span of time recognized by geologists; smaller than a eon, larger than a period.

We are currently in the Cenozoic era. Rocks of a specific era are called eratherms. Conodonts are another example of microfossils useful for biostratigraphic correlation of the Cambrian through Triassic Periods. Conodonts are tooth-like phosphatic structures of an eel-like multi-celled organism that had no other preservable hard parts. The conodont-bearing creatures lived in shallow marine environments all over the world.

Upon death, the phosphatic hard parts were scattered into the rest of the marine sediments. These distinctive tooth-like structures are easily collected and separated from limestone in the laboratory. Artist reconstruction of the conodont animal right along side its teeth Because the conodont creatures were so widely abundant, rapidly evolving, and readily preserved in sedimentstheir fossils are especially useful for correlating strataeven though knowledge of the actual animal possessing them is sparse.

Scientists in the s carried out a fundamental biostratigraphic correlation that tied Triassic conodont zonation into ammonoids, which are extinct ancient cousins of the pearly nautilus. Up to that point ammonoids were the only standard for Triassic correlationso cross-referencing micro- and macro- index fossils enhanced the reliability of biostratigraphic correlation for either type. That conodont study went on to establish the use of conodonts to internationally correlate Triassic strata located in Europe, Western North America, and the Arctic Islands of Canada.

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Geologic time on Earth, represented circularly, to show the individual time divisions and important events. Geologic time has been subdivided into a series of divisions by geologists. We are currently in the Phanerozoic eon. Rocks of a specific eon are called eonotherms.

The partitions of the geologic time scale is the same everywhere on Earth; however, rocks may or may not be present at a given location depending on the geologic activity going on during a particular period of time.

Thus, we have the concept of time vs. The figure of the geologic time scale, represents time flowing continuously from the beginning of the Earth, with the time units presented in an unbroken sequence. But that does not mean there are rocks available for study for all of these time units. The geologic time scale was developed during the 19 th century using the principles of stratigraphy.

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The relative order of the time units was determined before geologist had the tools to assign numerical ages to periods and events. Biostratigraphic correlation using fossils to assign era The second largest span of time recognized by geologists; smaller than a eon, larger than a period.

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With the expansion of science and technology, some geologists think the influence of humanity on natural processes has become so great they are suggesting a new geologic time perio known as the Anthropocene. Events in Earth history can be placed in sequence using the five principles of relative dating. The geologic time scale was completely worked out in the 19th Century using these principles without knowing any actual numeric ages for the events.

Accurately interpreting radioisotopic dating data depends on the type of rock tested and accurate assumptions about isotope baseline values. With a combination of relative and absolute datingthe history of geological events, age of Earth, and a geologic time scale have been determined with considerable accuracy. Stratigraphic correlation is additional tool used for understanding how depositional environments change geographically. Geologic time is vast, providing plenty of time for the evolution of various lifeforms, and some of these have become preserved as fossils that can be used for biostratigraphic correlation.

The geologic time scale is continuous, although the rock record may be broken because rocks representing certain time periods may be missing.

Christopher B. DuRoss, Stephen F. Personius, Anthony J. Crone, Susan S. Bulletin of the Seismological Society of America- Biogenic structures: Their use in interpreting depositional environments.

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Sepm Society for Sedimentary, Advances in Fission-Track Geochronology. Karen Chin. What did Dinosaurs Eat? Coprolites and other direct evidence of Dinosaur diets. James O Farlow, R. The Scientific Study of Dinosaur Footprints.

Martin Lockley. Tracking dinosaurs: a new look at an ancient world. MacDougall, Doug. Whewell, W. Parker, Berry, W. WH Freeman and Co, Mosher, L. Dickin, A. Radiogenic isotope geology. Cambridge University Press, Murray, A. Optically stimulated luminescence dating of sediments over the pastyears. Earth Planet. In its place, the particles that settle from the transporting medium will be finer-grained, and there will be a lateral transition from coarser- to finer-grained material.

The lateral variation in sediment within a stratum is known as sedimentary facies. If sufficient sedimentary material is available, it will be deposited up to the limits of the sedimentary basin.

Often, the sedimentary basin is within rocks that are very different from the sediments that are being deposited, in which the lateral limits of the sedimentary layer will be marked by an abrupt change in rock type.

Melt inclusions are small parcels or "blobs" of molten rock that are trapped within crystals that grow in the magmas that form igneous rocks. In many respects they are analogous to fluid inclusions. Melt inclusions are generally small - most are less than micrometres across a micrometre is one thousandth of a millimeter, or about 0.

Nevertheless, they can provide an abundance of useful information. Using microscopic observations and a range of chemical microanalysis techniques geochemists and igneous petrologists can obtain a range of useful information from melt inclusions.

Two of the most common uses of melt inclusions are to study the compositions of magmas present early in the history of specific magma systems. This is because inclusions can act like "fossils" - trapping and preserving these early melts before they are modified by later igneous processes.

In addition, because they are trapped at high pressures many melt inclusions also provide important information about the contents of volatile elements such as H 2 O, CO 2S and Cl that drive explosive volcanic eruptions. Sorby was the first to document microscopic melt inclusions in crystals. The study of melt inclusions has been driven more recently by the development of sophisticated chemical analysis techniques.

Scientists from the former Soviet Union lead the study of melt inclusions in the decades after World War II Sobolev and Kostyuk,and developed methods for heating melt inclusions under a microscope, so changes could be directly observed. Although they are small, melt inclusions may contain a number of different constituents, including glass which represents magma that has been quenched by rapid coolingsmall crystals and a separate vapour-rich bubble. They occur in most of the crystals found in igneous rocks and are common in the minerals quartzfeldsparolivine and pyroxene.

The formation of melt inclusions appears to be a normal part of the crystallization of minerals within magmas, and they can be found in both volcanic and plutonic rocks.

The law of included fragments is a method of relative dating in geology. Essentially, this law states that clasts in a rock are older than the rock itself. Another example is a derived fossilwhich is a fossil that has been eroded from an older bed and redeposited into a younger one. This is a restatement of Charles Lyell 's original principle of inclusions and components from his to multi-volume Principles of Geologywhich states that, with sedimentary rocksif inclusions or clasts are found in a formationthen the inclusions must be older than the formation that contains them.

These foreign bodies are picked up as magma or lava flowsand are incorporated, later to cool in the matrix. As a result, xenoliths are older than the rock which contains them Relative dating is used to determine the order of events on Solar System objects other than Earth; for decades, planetary scientists have used it to decipher the development of bodies in the Solar Systemparticularly in the vast majority of cases for which we have no surface samples.

Many of the same principles are applied. For example, if a valley is formed inside an impact craterthe valley must be younger than the crater. Craters are very useful in relative dating; as a general rule, the younger a planetary surface is, the fewer craters it has. If long-term cratering rates are known to enough precision, crude absolute dates can be applied based on craters alone; however, cratering rates outside the Earth-Moon system are poorly known. Relative dating methods in archaeology are similar to some of those applied in geology.

The principles of typology can be compared to the biostratigraphic approach in geology. From Wikipedia, the free encyclopedia. For relative dating of words and sound in languages, see Historical linguistics. Main article: Typology archaeology. Further information: Dating methodologies in archaeology.

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Earth System History. New York: W. Freeman and Company. The earth through time 9th ed. Hoboken, N. Dinosaurs and the History of Life. Columbia University. Archived from the original on Retrieved Armstrong, F. Mugglestone, R.

Laws of Relative Rock Dating

Richards and F. Belmont: Wadsworth Publishing Company. Periods Eras Epochs. Canon of Kings Lists of kings Limmu. Chinese Japanese Korean Vietnamese. Lunisolar Solar Lunar Astronomical year numbering.

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