It seems really farfetched to me, are we counting fossil rings or something?
In: Chemistry
radiation of certain things decay by half from time to time, and they know what is the average of radioactive isotopes for a common body, this way they can measure the ratio and discover the time
Close. Carbon dating is fairly accurate. The carbon element decays at a fixed rate very slow over a long period of time. Like if you hold a pair of really faded old jeans to an unworn replica.
I assume you mean fossils and organic matter. Organics and organisms are made of carbon. Carbon has a radioactive isotope C-14, which is made in the upper atmosphere after interactions of our atmosphere with cosmic rays. This C-14 isotope is absorbed by plants and other organisms and is incorporated in themselves. When these organisms are eaten by other organisms, they also get the C-14.
However, when an organism dies, it is no longer getting the C-14 isotope. As the C-14 isotope decays over time, it’s concentration in the remains of the organism becomes smaller and smaller. By measuring the observed concentration of C-14 in fossils or organic remains versus what would be expected if they were alive now, scientists can tell how long ago the organism died, thereby giving us radiocarbon dating.
There are various methods. Some things are discovered in geological strata that were formed a known time (or, really, range of times) ago. Other times, the date is derived from some form of radioisotope dating, often referred to as “carbon dating”. There is a known proportion of radioactive carbon and stable carbon in the world. Living things constantly exchange carbon with their environments, so they’re at that same proportion. When they die, they stop exchanging carbon with their environment, and the radioactive carbon in them decays at a known rate. By measuring what portion of the carbon within their remains is radioactive, we can calculate how long ago that thing died. It’s also possible to do things like analyze trapped pockets of gas, particularly in ice formations, to try to match them up with an atmospheric composition known to exist a certain time ago.
For learning about climate related events, ye, pretty much.
Not on fossils, but on pieces of ice. We can 3xtract really long columns of from the Arctic and Antarctic and look at the layers formed because ice melted when it was warmer and has a different texture. So you can tell stuff like lengths of seasons and stuff like that a really long time ago.
So, all biological matter has Carbon in it, and that Carbon will mostly be made from Carbon-12, but *some* of it will also be Carbon-14. Unlike Carbon-12, Carbon-14 is naturally unstable and eventually turns into Nitrogen-14. Thus, if you take a sample of an object and measure the amount of Carbon-14 in it, you can get a pretty reliable way to figure out how old that object actually is.
The only problem is that the object you’re testing has to be *known* to have been around before 1955 or so; atmospheric nuclear testing from 1955 to 1980 deposited a (relatively) large amount of new Carbon-14 all over the world, thus anyt biological material that grew after 1955 will have absorbed some of this new Carbon-14.
One of the most well-known methods is radiocarbon dating.
As you might know, all things are made up of atoms. At the center of every atom is something called a nucleus, which is made up of protons and neutrons. The exact number of protons and neutrons tells you what kind of atom it is.
Not all nuclei are created equal. Some of them are unstable, which means that when they’re formed, they start decaying, which changes the number of protons an neutrons in the nucleus.
Carbon-14 is one of these types of unstable elements. C-14 is constantly being created when high-speed particles in space collide with atoms in our atmosphere. Since C-14 is unstable, it starts to decay as soon as it’s created.
C-14 is everywhere, and plants constantly absorb it when they absorb carbon dioxide. Then, it gets into animals when they eat the plants.
When a plant or animal is alive, they’re constantly absorbing new C-14. But when they die, they stop.
Scientists can analyze a sample and check how much C-14 is in it. In a very old sample, a lot of the C-14 will have decayed. A newer sample will have more of it.
>are we counting fossil rings or something?
You can actually do something very similar to that with layers of earth. Just like trees add rings, new layers of rock are constantly being formed and buried. By determining which layer of rock you find a fossil in, you can make assumptions about its age.
It’s possible to date some substances very accurately. One example is using Potassium-Argon to date volcanic rocks.
When molten rock solidifies, it will usually form a crystal structure. Ordinary, argon will not form part of this structure; it’s a noble gas and thus doesn’t interact with other elements strongly enough.
However potassium will participate in forming that crystal… and one of it’s isotopes (Potassium-40) is unstable and decays to Argon-40. When that happens, the argon is trapped in the crystal. The ratio of Potassium-40 to Argon-40 in the rock allows you to figure out how long it was since the molten rock cooled. When the rock is newly formed, there’s almost no Argon-40 in it. After about a billion years, there will be a 10:1 ratio Potassium-40:Argon-40.
Once you’ve found the absolute age of something, you can then date things relative to that. Find the fossil of some poor dinosaur that got caught in a lava flow, and date the lava flow? Well obviously that dinosaur was alive at about the same time as the rock was formed. Find another fossil of the same species of dino somewhere else…that fossil was probably buried within a couple hundred thousand years of the first one, so now you have a good idea of how old the rock around the second fossil is, and the age of other fossils in that geological layer.
You can also use less precise methods relative to your precisely measured date. think of those methods like pacing out a distance. Errors add up over long distances, so trying to pace out the length of a mile might be pretty tricky. If your off by 10%, that’s a pair of football fields. Find a highway marker tell you that your standing at 1700 yards from your starting point…now you only need to measure the last 60 yards. Even if you’re wrong by a huge margin, the total error is small because you know most of the distance very accurately.
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