Dating Techniques

The Radiometric Dating Game Radiometric dating methods estimate the age of rocks using calculations based on the decay rates of radioactive elements such as uranium, strontium, and potassium. On the surface, radiometric dating methods appear to give powerful support to the statement that life has existed on the earth for hundreds of millions, even billions, of years. We are told that these methods are accurate to a few percent, and that there are many different methods. We are told that of all the radiometric dates that are measured, only a few percent are anomalous. This gives us the impression that all but a small percentage of the dates computed by radiometric methods agree with the assumed ages of the rocks in which they are found, and that all of these various methods almost always give ages that agree with each other to within a few percentage points. Since there doesn’t seem to be any systematic error that could cause so many methods to agree with each other so often, it seems that there is no other rational conclusion than to accept these dates as accurate. However, this causes a problem for those who believe based on the Bible that life has only existed on the earth for a few thousand years, since fossils are found in rocks that are dated to be over million years old by radiometric methods, and some fossils are found in rocks that are dated to be billions of years old.

Copy of Relative Dating: The Age of Rock Layers by Brian Ferrenz on Prezi

Law of Superposition on top is younger Intrusions magma inside Earth. Extrusions magma on top of Earth. Faults breaks in the crust Unconformities signs of erosion. Whether your application is business, how-to, education, medicine, school, church, sales, marketing, online training or just for fun, PowerShow.

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Timeline of Life on Earth Evolution is a complicated subject. While everybody understands that black bears are related to grizzly bears and we can even figure they are related to extinct bears, lots of people wonder how scientists can be so sure that bears are related to salmon as well. Basically, scientists have learned that rocks are stacked in layers containing fossils with the oldest fossils at the deepest layers, and the youngest, or most recent fossils, near the top. It’s as if rock layers are a vertical timeline.

At the bottom of the timeline there are no fossils of modern animals. As you move towards the surface, you find fish, then amphibians, then reptiles, mammals, birds, and finally modern mammals including humans. We’re not talking about an abstract diagram: But how do we know this evolutionary sequence of layers, one on top of the other, is accurate?


Student Reading Pick up a rock, any rock, and examine it. Can you see any way to determine its age? Is it ten years or ten million years old? You cannot tell just by looking at it. For this reason, scholars for nearly all of human history had no way of knowing the age of the Earth or its rocks.

with your students to a nearby outcrop of rock layers, whether a riverbank, valley wall, or distant view of a volcano. Bring appropriate blocks, such as. stream gravels, glacial deposits, etc. Instruct students to place blocks directly on the layer be? Make an analogy to Carbon dating.

When looking more deeply into its rock layers, like leafing through the pages of a book, one can read about a wealth of palaeoevinromental and biological processes. The Karoo Basin is an invaluable archive of information over its million year depositional history. Rich in fossils, both plants and animals, the Karoo Basin records crisis periods — mass extinction events — in the distant past when many species became extinct. So far, there have been five main mass extinction events globally.

The Karoo Basin also holds evidence of the third largest mass extinction. This occurred at the end of the Triassic, about million years ago, and heralded the rise of the dinosaurs. Understanding these climate change events and their impact on biology in the Karoo Basin could influence the way we look at the sixth extinction, which is happening now: Scientists need to know when the ancient extinctions happened and for how long.

These events are recorded in layers of rock. So we need to know the age of those rocks. Fossil pollen and spores are others. But when these are scarce, we need another way of measuring the age of rocks. A different technique My colleagues and I were interested in the age of a specific rock unit in the Karoo Basin: Rocks of the Elliot Formation outcrop in a ring around the Drakensberg Plateau see figure.

Relative Dating Rock Layers

Glossary Terms Introduction Stratigraphy is the study of rock layers and reconstruction of the original sequence in which they were deposited. The stratigraphy of an area provides the basis for putting together the geologic history of an area. The details of a region’s stratigraphic story are revealed by: What exactly is in each stratum layer — the types of rocks and minerals, the sedimentary structure , and the fossils. This reveals what was happening at the time the layer of sediment was being deposited in terms of geological activity, water, climate, and living things The sequence of strata — which layer is on top of which.

If a layer of rock containing the fossil is higher up in the sequence that another layer, you know that layer much be younger in age. By combining these principals, relative dating techniques can usually be used to determine the approximate age of a fossil.

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How we used the Earth’s magnetic field to date rocks rich in dinosaur fossils

When layers A-B-C were present, intrusion D formed. Intrusion D cut through layers A-C. Fault E formed, shifting rocks A through C and intrusion D. Weathering and erosion occurred, forming a layer of soil on top of layer A. Unconformities in Rock Layers[ edit ] Steno discovered the rules for determining the relative age of rock beds, but he did not have a good understanding of how long it would take for these rock formations to form. At the time, most Europeans believed that the Earth was around 6, years old, a figure that was based on the amount of time estimated for the events described in the Bible.

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Dating methods Dating techniques are procedures used by scientists to determine the age of a specimen. Relative dating methods tell only if one sample is older or younger than another sample; absolute dating methods provide a date in years. The latter have generally been available only since Many absolute dating techniques take advantage of radioactive decay , whereby a radioactive form of an element is converted into another radioactive isotope or non-radioactive product at a regular rate.

Others, such as amino acid racimization and cation-ratio dating, are based on chemical changes in the organic or inorganic composition of a sample. In recent years, a few of these methods have undergone continual refinement as scientists strive to develop the most accurate dating techniques possible. Relative dating methods determine whether one sample is older or younger than another. They do not provide an age in years.

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It is widely accepted that the Earth is about 4. There are two techniques geologist use to obtain the Earth’s age: Radioactive dating and Relative dating. We will discuss radioactive data later. Many rock formations are layered. For example, the Colorado river has eroded away parts of the Columbia plateau.

Why does relative age dating require undisturbed rock layers. To arrange geological events, the principle of past in. Superposition- in which is a fossil or fossil by studying the law of strata, rock layers and interpret the age to top.

Scientific measurements such as radiometric dating use the natural radioactivity of certain elements found in rocks to help determine their age. Scientists also use direct evidence from observations of the rock layers themselves to help determine the relative age of rock layers. Specific rock formations are indicative of a particular type of environment existing when the rock was being formed.

For example, most limestones represent marine environments, whereas, sandstones with ripple marks might indicate a shoreline habitat or a riverbed. The study and comparison of exposed rock layers or strata in various parts of the earth led scientists in the early 19th century to propose that the rock layers could be correlated from place to place. Locally, physical characteristics of rocks can be compared and correlated.

On a larger scale, even between continents, fossil evidence can help in correlating rock layers. The Law of Superposition, which states that in an undisturbed horizontal sequence of rocks, the oldest rock layers will be on the bottom, with successively younger rocks on top of these, helps geologists correlate rock layers around the world. This also means that fossils found in the lowest levels in a sequence of layered rocks represent the oldest record of life there. By matching partial sequences, the truly oldest layers with fossils can be worked out.

Relative Dating – Example 1

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