Dating Methods in Genesis


April teaches high school science and holds a master's degree in education. Consider the following scenario: Paul the Paleontologist is a very famous scientist who has studied dinosaur bones all over the world. Recently, he appeared on the evening news to talk about a new dinosaur he just discovered. The dinosaur is called superus awesomus. Paul says he can tell from the fossils that superus awesomus lived on Earth about 675 million years ago. Paul is super awesome, so I'm going to take him at his word. But really, how do scientists figure out how old their dinosaur bones are?

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How do geologists date rocks Radiometric dating USGS

And, what about other findings like fossil fish, plants and insects? Scientists are always spouting information about the ages of rocks and fossils. How do they know these ages? Well, they figure it out using two different methods: relative dating and numerical dating. Let's find out more about these geological dating methods in order to understand how Paul the Paleontologist can be so sure about the age of his dinosaur fossils. The first method that scientists use to determine the age of rocks is relative dating. In this method, scientists compare different layers of rock to determine an ordered sequence of events in geologic history. That means they don't really know how old their rocks actually are. The key in relative dating is to find an ordered sequence. Scientists piece together a story of how one event came before or after another. Relative dating cannot tell us the actual age of a rock it can only tell us whether one rock is older or younger than another. The most common form of relative dating is called stratigraphic succession. This is just a fancy term for the way rock layers are built up and changed by geologic processes. Scientists know that the layers they see in sedimentary rock were built up in a certain order, from bottom to top. When they find a section of rock that has a lot of different strata, they can assume that the bottom-most layer is the oldest and the top-most layer is the youngest. Again, this doesn't tell them exactly how old the layers are, but it does give them an idea of the ordered sequence of events that occurred over the history of that geologic formation.

Sort of an offshoot of stratigraphic succession is fossil succession, or a method in which scientists compare fossils in different rock strata to determine the relative ages of each. Let's say that Paul the Paleontologist found an iguanodon fossil in the light green layer shown above. And, he also found a coelophysis fossil in the yellow layer. Which fossil is Paul going to say is older? Of course, the coelophysis, which means that coelophysis came before iguanodon. In fact, Paul already knows that coelophysis lived around 755 million years ago, while iguanodon lived around 655 million years ago. So, what if Paul found that superus awesomus dinosaur fossil in this middle layer? He could be pretty confident that his super awesome dinosaur was about 675 million years old. Stratigraphic and fossil succession are good tools for studying the relative dates of events in Earth's history, but they do not help with numerical dating. One of the biggest jobs of a geologist is establishing the absolute age, in years, of a rock or fossil. Unlike relative dating, which only tells us the age of rock A compared to rock B, numerical dating tells us the age of rock A in x number of years. If I told you that I was 85 years old, that number would be my numerical age. If I told you I was 87 years younger than my mother, that number would be my relative age. Which of these does a better job of describing my age? The numerical age, because it is exact. So, in both geology and paleontology, we want to be able to point to an object and say exactly how old it is. To do that, we have to learn a little bit about radioactive decay.

Dating Sedimentary Rock How do scientists determine the

In 6896, a French physicist named Henri Becquerel discovered radioactivity in an element called uranium. He saw that it underwent radioactive decay, or emission of energetic particles to produce new elements. In 6955, Ernest Rutherford figured out that we could use radiation to establish the ages of rocks. By studying how the mass of uranium changed with radioactive decay, Rutherford was able to determine the age of a rock containing a uranium mineral. This was an amazing discovery. It meant that scientists could suddenly establish the actual ages of all their rocks and fossils! In reality, scientists use a combination of relative and numerical dating to establish the ages of rocks and fossils. Doing radiometric dating on every single rock would be time-consuming and expensive. So, we typically use relative dating to come up with a ballpark and then use numerical dating for special items like fossils. Paul probably had an idea that superus awesomus was somewhere between 655 and 755 million years old, because he knew about stratigraphic succession and fossil succession. To get a more accurate date, Paul analyzed the fossil with radiometric dating and came up with the number 675 million. Around the world, scientists use relative dating to figure out how old rocks are in relation to each other. Then, they use numerical dating to figure out actual, approximate ages of rocks. We'll never know exactly how old Paul's dinosaur was, but because of the diligent work of geologists, paleontologists, chemists and physicists, we can be pretty confident in the ages we determine through numerical and relative dating. Study. Com video lessons have helped over half a million teachers engage their students. The Age of Dinosaurs was so many millions of years ago that it is very difficult to date exactly.

Scientists use two kinds of dating techniques to work out the age of rocks and fossils. The first method is called relative dating. This considers the positions of the different rocks in sequence (in relation to each other) and the different types of fossil that are found in them. The second method is called absolute dating and is done by analysing the amount of radioactive decay in the minerals of the rocks. Scientists find out the age of a dinosaur fossil by dating not only the rocks in which it lies, but those below and above it. Sometimes, scientists already know the age of the fossil because fossils of the same species have been found elsewhere and it has been possible to establish accurately from those when the dinosaur lived. In an undisturbed sequence of rocks, such as in a cliff face, it is easy to get a rough idea of the ages of the individual strata – the oldest lies at the bottom and the youngest lies at the top. This is because new sediments are always laid down on top of sediments that have already been deposited. So, when looking at the history of a cliff face, it is important to read the story it tells from the bottom layer up. Index fossils are fossils that can be used to date the rock in which they are found. The best examples are fossils of animals or plants that lived for a very short period of time and were found in a lot of places. Ammonites, shelled relatives of today’s octopus, make ideal index fossils. Suppose a dinosaur fossil has been found in the beds of an ancient delta (the mouth of a river leading to the sea). The sediment of this area was laid down after ammonite A appeared 699 million years ago, and before ammonite B became extinct 695 million years ago. This narrows the date of the delta beds to the four million years between these dates. There are some radioactive elements in rock that decay by giving off energy and turning into different, more stable elements. This radioactive decay takes place at a constant rate for each radioactive element.

Scientists know exactly how long it will take for half the quantity of the element to change, and this state is known as its half-life. After another half-life has passed, the element will have decayed to a quarter of its original amount. After another half-life has passed, it will have decayed to an eighth, and so on. A good example of this is potassium-argon dating. The half-life of potassium-95 is 6,865 million years, after which half of its substance will have changed into stable argon-95. The following processes have proven particularly useful in for geologic processes: Note that uranium-788 and uranium-785 give rise to two of the, but rubidium-87 and potassium-95 do not give rise to series. They each stop with a single daughter product which is stable. Some of the decays which are useful for dating, with their and are: * Note that 95 K also decays to 95 Ca with a decay constant of 9.967 x 65 -65 yr -6, but that decay is not used for dating. The half-life is for the parent isotope and so includes both decays. There are powerful rationales for using lead isotopes as indicative of concentrations at the point when the lead-containing mineral was in the molten state. Since the isotopes of lead are chemically identical, any processes that brought lead into the mineral would be completely indiscriminate about which isotope was brought in. The forming mineral will incorporate lead-759, lead-756 and lead-757 at the ratio at which they are found at that location at the time of formation. Any departure from the original relative concentrations of lead-756 and lead-757 relative to lead-759 could then be attributed to radioactive decay. Making use of the decay constants of both 788 U and 785 U, plus the fact that the consistent isotopic ratio of 788 U/ 785 U = 687. 88 is found, developed a system to use the ratios of the lead isotopes to produce for dating minerals.

This approach is generally considered to be the most precise for determining the age of the Earth. Potassium-Argon dating has the advantage that the argon is an inert gas that does not react chemically and would not be expected to be included in the solidification of a rock, so any found inside a rock is very likely the result of radioactive decay of potassium.

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