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This page has been archived and is no longer updated. Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4. Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free. These changes typically occur so slowly that they are barely detectable over the span of a human life, yet even at this instant, the Earth's surface is moving and changing. As these changes have occurred, organisms have evolved, and remnants of some have been preserved as fossils.
This sediment eventually settles on the bottom of lake beds or deposits at the mouth of rivers in an alluvial fan. This process of material deposition and erosion as well as the rise and fall in the lake levels due to environmental changes slowly added layers to the geologic record found in the Turkana Basin.
Over time the sediment solidified into rock. Bones of ancient humans, our hominin ancestors, and other animal species were buried in the sediment, and eventually became fossilized and preserved in the rocks. In the Koobi Fora formation, bands of sedimentary rock are interspersed with layers of tuffa sign of times when tectonic and volcanic activity dominated the landscape.
After completing this lesson, you will be able to explain radiometric dating, and index fossils, and how we use a combination of the two to figure. Radiometric dating. Geologists use radiometric dating to estimate how long ago rocks formed, and to infer the ages of fossils contained within those rocks. Carbon, Radiometric Dating and Index Fossils. Carbon dating is used to determine the age of biological artifacts up to 50, years old. This technique is .
Typically, the ash, pumiceand other materials that spew from volcanoes either fall straight back to the earth or are carried away by air currents or rivers and streams. This volcanic matter eventually settles and over time is compacted to form a special type of sedimentary rock called tuff.
Tectonic activity has had other impacts on research in Koobi Fora region. During the Pliocene geologic epoch 5. This allowed for erosional forces to expose rock that was buried long ago. These processes also exposed the fossils buried within those layers of rock.
The layers of volcanic rock are extremely important to reconstructing the history of the Turkana Basin because they allow scientists to calculate the age of hominin fossils found in the region.
The volcanic material in tuff is well-suited for radiometric datingwhich uses known decay rates for specific unstable isotope s to determine the age of the rock that contains that isotope. Feldspar crystals found in the tuff layers contain an unstable isotope of potassium that can be used for this dating method. The field of archeology often uses carbon isotopes, which are much more common, but the field of paleontology often uses a potassium- argon dating technique because it can be used to date much older rock material.
Over time, the unstable potassium isotope 40 K from the rocks decay into a stable isotope of argon 40 Ar. The ratio of the stable argon isotope formed from decay to the unstable potassium isotopes tells scientists when the tuff layer cooled and solidified into rock.
Knowing the dates of the tuff, scientists can then estimate a date for the fossils. Fossils above a specific layer are inferred to be younger than that layer, and those below are older, in line with the law of superposition, a key scientific principle of stratigraphy. Dating of the fossils contributes to a clearer timeline of evolutionary history.
Older methods of dating were more subjective, often an educated hypothesis based on the evidence available. However, the fossils in the Turkana region can be dated more accurately because they are found in the sedimentary rock between datable layers of tuff.
Although radiometric dating of the tuff is scientifically valid, difficulties still exist. Extending the Learning The fossils found in the Turkana Basin support the theory of human evolution and the theory that humans originated in Africa before migrating to other places. Consider the age and different species of fossils found in the area.
Using your knowledge of evolutionary theory, construct an argument that explains these connections. Examine the stratigraphic column diagram. What relationship seems to exist between the approximate age of the fossils and rocks layers and their depth in the earth?
Following the law of superposition in geology, older fossils and rocks are found in lower strata than younger fossils and rock layers. Tectonic activity left some areas of land upliftedand erosional forces from the lake, nearby rivers, and other forms of weathering exposed rock, even older rock layers, as outcroppings in the landscape. This made the fossils easier for researchers to find.
The volcanic material in tuff layers also makes it possible to get a more accurate date for the fossils. Potassium-argon dating is a form of isotopic dating commonly used in archaeology.
Scientists use the known natural decay rates for isotopes of potassium and argon to find the date of the rocks. The radioactive isotope converts to a more stable isotope over time, in this case decaying from potassium to argon.
If scientists find the ratio of potassium to argon, it tells them how long the rocks have been around by how long the isotopes have been decaying. By understanding the dates of these rocks, scientists can deduce the age of the nearby fossils.
What difficulties might paleontologists and archaeologists have when trying to find and date fossils? There are many possible answers. One answer based on a common problem encountered by scientists is that fossils are often encased in rocks or are similarly colored, so they blend in with their surroundings.
Sometimes, only a small part of a fossil is showing. They might also be buried. Because of these characteristics, field crews have to carefully examine their surroundings to find possible fossils.
There are several common radioactive isotopes that are used for dating rocks, artifacts and fossils. The most common is U U is found in many igneous . How are fossils and other findings analyzed in Kenya's Turkana Basin? The volcanic material in tuff is well-suited for radiometric dating. Scientists find out the age of a dinosaur fossil by dating not only the rocks in which There are some radioactive elements in rock that decay by giving off energy.
Fossils might also be fragile or found in small fragments. Archaeologists have to use their skill and patience to put small pieces back together, like a jigsaw puzzle.
Although fossil dating is now more scientifically accurate, it still requires skill and experience as scientists have to make educated guesses based on any evidence and the dating available for the layers surrounding the fossils. Why is a unique fossil name like this important? Because each name is a unique identification, this helps scientists keep track of where and in what order fossils are found.
Doing this helps paleontologists maintain accurate records and piece together the story of human history.
The accompanying numbers are chronologicalmeaning that, in this example, our fossil is the 1,th fossil found in the area. Also called an extensional boundary. Human beings are the only living hominins.
A hypothesis is tested to determine if it is accurate. Also called radioactive dating.
Radiometric Dating with Index Fossils
Also called lithospheric plate. Also called a radionuclide. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited. Carbon cannot be used to date biological artifacts of organisms that did not get their carbon dioxide from the air.
This rules out carbon dating for most aquatic organisms, because they often obtain at least some of their carbon from dissolved carbonate rock. The age of the carbon in the rock is different from that of the carbon in the air and makes carbon dating data for those organisms inaccurate under the assumptions normally used for carbon dating. This restriction extends to animals that consume seafood in their diet. As stated previously, carbon dating cannot be used on artifacts over about 50, years old.
These artifacts have gone through many carbon half-lives, and the amount of carbon remaining in them is miniscule and very difficult to detect. Carbon dating cannot be used on most fossils, not only because they are almost always allegedly too old, but also because they rarely contain the original carbon of the organism that has been fossilized.
18.5D: Carbon Dating and Estimating Fossil Age
Also, many fossils are contaminated with carbon from the environment during collection or preservation procedures. Scientists attempt to check the accuracy of carbon dating by comparing carbon dating data to data from other dating methods. Other methods scientists use include counting rock layers and tree rings.
When scientists first began to compare carbon dating data to data from tree rings, they found carbon dating provided "too-young" estimates of artifact age. Scientists now realize that production of carbon has not been constant over the years, but has changed as the radiation from the sun has fluctuated.
Nuclear tests, nuclear reactors and the use of nuclear weapons have also changed the composition of radioisotopes in the air over the last few decades. This human nuclear activity will make precise dating of fossils from our lifetime very difficult due to contamination of the normal radioisotope composition of the earth with addition artificially produced radioactive atoms.
The various confounding factors that can adversely affect the accuracy of carbon dating methods are evident in many of the other radioisotope dating methods. Although the half-life of some of them are more consistent with the evolutionary worldview of millions to billions of years, the assumptions used in radiometric dating put the results of all radiometric dating methods in doubt.
The following is an article on this subject. Although the half-life of carbon makes it unreliable for dating fossils over about 50, years old, there are other isotopes scientists use to date older artifacts.
These isotopes have longer half-lives and so are found in greater abundance in older fossils. All of these methods are accurate only back to the last global catastrophe i.
Absolute dating is used to determine a precise age of a fossil by using radiometric dating to measure the decay of isotopes, either within the fossil or more often. Using relative and radiometric dating methods, geologists are able to answer the question: how old is this fossil?. Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change.
The assumptions are similar to the assumptions used in carbon dating. The mathematical premise undergirding the use of these elements in radiometric dating contains the similar confounding factors that we find in carbon dating method.
Most scientists today believe that life has existed on the earth for billions of years.
This belief in long ages for the earth and the evolution of all life is based entirely on the hypothetical and non-empirical Theory of Evolution. All dating methods that support this theory are embraced, while any evidence to the contrary, e. Prior to radiometric dating, evolution scientists used index fossils a. A paleontologist would take the discovered fossil to a geologist who would ask the paleontologist what other fossils searching for an index fossil were found near their discovery.
If it sounds like circular reasoning, it is because this process in reality is based upon circular reasoning. The process of using index fossils is describes by the late Creationist author and Ph.Radioactive Dating
Henry Morris as follows:. Michael Oard, Ph. All radiometric dating methods use this basic principle to extrapolate the age of artifacts being tested.
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, leadso the higher the ratio of lead to uranium, the older the rock must be.
While there are many problems with such dating methods, such as parent or daughter substances entering or leaving the rock, e. Geologists assert that generally speaking, older dates are found deeper down in the geologic column, which they take as evidence that radiometric dating is giving true ages, since it is apparent that rocks that are deeper must be older. But even if it is true that older radiometric dates are found lower down in the geologic column which is open to questionthis can potentially be explained by processes occurring in magma chambers which cause the lava erupting earlier to appear older than the lava erupting later.
Lava erupting earlier would come from the top of the magma chamber, and lava erupting later would come from lower down. A number of processes could cause the parent substance to be depleted at the top of the magma chamber, or the daughter product to be enriched, both of which would cause the lava erupting earlier to appear very old according to radiometric dating, and lava erupting later to appear younger.
Fossils and radiometric dating
Other possible confounding variables are the mechanisms that can alter daughter-to-parent ratios. We can see that many varieties of minerals are produced from the same magma by the different processes of crystallization, and these different minerals may have very different compositions. It is possible that the ratio of daughter to parent substances for radiometric dating could differ in the different minerals.
Clearly, it is important to have a good understanding of these processes in order to evaluate the reliability of radiometric dating. Other confounding factors such as contamination and fractionation issues are frankly acknowledged by the geologic community, but are not taken into consideration when the accuracy and validity of these dating methods are examined. The following quotation from Elaine G.
Kennedy addresses this problem. Contamination and fractionation issues are frankly acknowledged by the geologic community. For example, if a magma chamber does not have homogeneously mixed isotopes, lighter daughter products could accumulate in the upper portion of the chamber.