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This has been archived and is no longer updated.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.

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This diagram shows a selection of rock layers, or stratigraphic columns, from the Koobi Fora geologic formation on the eastern shore of Lake Turkana in Kenya. This area is a ridge of sedimentary rock where researchers have found more than 10, fossils, both human and other hominins, since These fossils aid the scientific investigation of human evolution.

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 pastyears. The current environment around Lake Turkana is very dry. Over Absolute dating fossils course of time, though, the area has seen many changes.

The climate of the region was once more humidwhich may have been favorable for early humans and hominins to have flourished there. All lakes, rivers, and streams carry sediment such as soil, sand, and volcanic matter. 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.

Dating fossils – how are fossils dated?

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 of times when tectonic and volcanic activity dominated the landscape. 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 the 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 datingAbsolute dating fossils uses known decay rates for specific unstable isotopes 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.

Dating fossils in the rocks

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 decays 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.

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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.

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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.

How do scientists date fossils?

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 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. 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.

Dating dinosaurs and other 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.

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Because of these characteristics, field crews have to carefully examine their surroundings Absolute dating fossils find possible fossils. 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 s 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. Also called lithospheric plate.

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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 that contains the media credit. The Rights Holder for media is the person or group credited. Sean P. Jill Wertheim, National Geographic Society.

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The rock cycle is a web of processes that outlines how each of the three major rock types—igneous, metamorphic, and sedimentary—form and break down based on the different applications of heat and pressure over time. For example, sedimentary rock shale becomes slate when heat and pressure are added.

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. The fossil record helps paleontologists, archaeologists, and geologists place important events and species in the appropriate geologic era.

It is based on the Law of Superposition which states that in undisturbed rock sequences the bottom layers are older than the top layers. Therefore, some discovered fossils are able to be dated according to the strata, a distinct layer of rock, that they are found in. Another common way that fossils are dated, is through radiocarbon dating. The development of this type of dating, in the s, transformed paleontology and enhanced the accuracy of the fossil record. With Absolute dating fossils new fossil discovery, our understanding of the environment in a particular time becomes richer.

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

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In the mids, Charles Darwin famously described variation in the anatomy of finches from the Galapagos Islands. 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.

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