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Lake Turkana has a geologic history that favored the preservation of fossils. Scientists suggest that the lake as it appears today has only been around for the past , years. The current environment around Lake Turkana is very dry. Over the course of time, though, the area has seen many changes. Over time the sediment solidified into rock.

Potassium-argon dating is a form of isotopic dating commonly used in paleontology. 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. Fossils Record Relative Time Prior to the 20th century, geologists could only determine the relative ages of rocks - whether one was younger or older than another. Working in the Bath district of western England, William Smith (-), an engineer and surveyor, saw that rock layers could be dated. May 18,   Relative dating The method of reading the order is called stratigraphy (layers of rock are called strata). Relative dating does not provide actual numerical dates for the rocks. Next time you find a cliff or road cutting with lots of rock strata, try working out the age order using some simple principles.

Each of them typically exists in igneous rock, or rock made from cooled magma. Fossils, however, form in sedimentary rock - sediment quickly covers a dinosaur's body, and the sediment and the bones gradually turn into rock. But this sediment doesn't typically include the necessary isotopes in measurable amounts. Fossils can't form in the igneous rock that usually does contain the isotopes.

Absolute dating is used to determine a precise age of a rock or fossil through radiometric dating methods. This uses radioactive minerals that occur in rocks and fossils almost like a geological clock. It's often much easier to date volcanic rocks than the fossils themselves or the sedimentary rocks they are found in.

The extreme temperatures of the magma would just destroy the bones. So to determine the age of sedimentary rock layers, researchers first have to find neighboring layers of Earth that include igneous rock, such as volcanic ash.

These layers are like bookends - they give a beginning and an end to the period of time when the sedimentary rock formed. By using radiometric dating to determine the age of igneous bracketsresearchers can accurately determine the age of the sedimentary layers between them. Using the basic ideas of bracketing and radiometric dating, researchers have determined the age of rock layers all over the world.

This information has also helped determine the age of the Earth itself. While the oldest known rocks on Earth are about 3.

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Based on the analysis of these samples, scientists estimate that the Earth itself is about 4. The more heat and pressure you add, the further the rock metamorphoses until it becomes gneiss. If it is heated further, the rock will melt completely and reform as an igneous rock.

Empower your students to learn about the rock cycle with this collection of resources. Another common way that fossils are dated, is through radiocarbon dating.

Use these resources to teach middle schoolers more about the fossil record and radiocarbon dating.

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Alfred Russel Wallace noted the similarities and differences between nearby species and those separated by natural boundaries in the Amazon and Indonesia. Independently they came to the same conclusion: over generations, natural selection of inherited traits could give rise to new species. Use the resources below to teach the theory of evolution in your classroom.

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Where did we come from? Humans continue to search for the answer to this fundamental question. Innovators of their time, Charles Darwin and Alfred Russel Wallace, used science to explain where humans came from, posing the theory of evolution.

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Evolutionary science and archaeology continue today. Use these materials in your classroom to teach your students about the origins of the homo sapien. Lake Turkana in Kenya has only been around for the pastyears, but the expanding and receding shores of the lake have provided food and water to organisms for millions of years. Today, scientists study the stratigraphy of the Turkana basin to better understand the age of fossils discovered there.

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Discoveries at Lake Turkana reveal information about the history of human evolution. Skip to content. How has tectonic activity influenced discoveries at Turkana? What is one technique that scientists use to date the fossils they find?

General considerations

InDanish naturalist Nichlaus Steno put forth the idea that horizontal layers of sedimentary rock represent a time sequence of Earth's geologic history. He realized that older layers of sedimentary rocks are deeper in the earth, and younger ones build on top of them.

Dating metamorphic rocks Should a simple igneous body be subjected to an episode of heating or of deformation or of a combination of both, a well-documented special data pattern develops. With heat, daughter isotopes diffuse out of their host minerals but are incorporated into other minerals in the rock. Surface exposure dating is a collection of geochronological techniques for estimating the length of time that a rock has been exposed at or near Earth's surface. 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 environments.

In geology, this is called the law of superposition. Stratigraphic analysis of the geology in the Lake Turkana region of Kenya showed that landscape has changed over time, and at times there was no lake present at all.

Modern Lake Turkana has only been around for aroun years. In addition to those fossils found at Koobi Fora, hominin fossils have been found in three other parts of the Turkana Basin. In the 19th and 20th centuries, some researchers thought Asia rather than Africa held the origins of man, and they investigated dragon bones fossilized teeth and bones found in China. One site, Dragon Bone Hill, led to the excavation of Homo erectus remains many call Peking man, which date back to roughlyyears ago.

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Rock formations or regions, such as Koobi Fora, are often given names based on descriptions, local names, or geographic features.

The term Koobi Fora comes from the language of the Gabra people who live near the site.

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This term describes the area by listing some of its vegetation Koobi Fora means a place of the commiphora, a source of myrrh. Great Rift Valley system. Media Credits 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.

Writer Cayla A. Media If a media asset is downloadable, a download button appears in the corner of the media viewer. Text Text on this page is printable and can be used according to our Terms of Service. Interactives Any interactives on this page can only be played while you are visiting our website. Surface exposure dating is used to date glacial advances and retreatserosion history, lava flows, meteorite impacts, rock slides, fault scarpscave development, and other geological events.

It is most useful for rocks which have been exposed for between 10 years and 30, years [ citation needed ]. The most common of these dating techniques is Cosmogenic radionuclide dating [ citation needed ].

Earth is constantly bombarded with primary cosmic rayshigh energy charged particles - mostly protons and alpha particles. These particles interact with atoms in atmospheric gases, producing a cascade of secondary particles that may in turn interact and reduce their energies in many reactions as they pass through the atmosphere.

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This cascade includes a small fraction of hadrons, including neutrons. In rock and other materials of similar density, most of the cosmic ray flux is absorbed within the first meter of exposed material in reactions that produce new isotopes called cosmogenic nuclides.

At Earth's surface most of these nuclides are produced by neutron spallation.

Dating Fossils - How Are Fossils Dated?

Using certain cosmogenic radionuclidesscientists can date how long a particular surface has been exposed, how long a certain piece of material has been buried, or how quickly a location or drainage basin is eroding.

The cumulative flux of cosmic rays at a particular location can be affected by several factors, including elevation, geomagnetic latitude, the varying intensity of the Earth's magnetic fiel solar winds, and atmospheric shielding due to air pressure variations. Rates of nuclide production must be estimated in order to date a rock sample. These rates are usually estimated empirically by comparing the concentration of nuclides produced in samples whose ages have been dated by other means, such as radiocarbon datingthermoluminescenceor optically stimulated luminescence.

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The excess relative to natural abundance of cosmogenic nuclides in a rock sample is usually measured by means of accelerator mass spectrometry.

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