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Reference fossils are remains of long-dead animals and plants that lived at a known time in history.If we know from radiometric dating that an animal only existed for a particular period of a few million years, we know that whenever we see that animal in a rock face, that part of the rock must have that particular age.
Because of this, when we look at a rock-face, we know that the bottom layers are the oldest, and that fossils parallel to each other along the layers of sediment are likely to be from the same era.Reference fossils are the remnants of dead animals and plants that we know existed at a particular time in history.If we see one of these fossils in a layer of rock, this tells us how old that rock must be.The nice thing is that this happens in a predictable pattern.The amount that decays into other elements can be predicted; the more years pass, the more will be broken down.When we look at a rock face, we know that the lower layers are colder.
But we can get more detailed information using these two methods.
After completing this lesson, you will be able to explain radiometric dating, and index fossils, and how we use a combination of the two to figure out the ages of rocks and fossils. Radiometric dating is a method used to figure out how old rocks are by looking at the amount of certain radioactive isotopes present in the sample.
But that probably sounds a bit complex, so let's start with some basics.
Radiometric dating is where we look at the amount of certain radioactive isotopes to figure out how old a rock is.
We know the amount of radioactive substance when the rock was formed, and we know how fast it decays into other non-radioactive substances, so we can look at the amounts in each rock and use it to calculate how old the rock is.
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