I claim that ages of rocks tell us many things about earth’s past, including what life was like, what the climate was like, how the rocks were formed, how old they are relative to each other.
Fossils can help us with geologic history by telling us what time period the rocks around them were. When an animal dies, it has the small chance to turn into a fossil. It can be fossilized in tree sap and become amber, or it can be buried, and the bones can fill with microscopic sediment and become rocks. Once the fossils are formed, they can stay in the same rock for millions of years before they finally become exposed, and found by archeologists. Archeology and geology are very similar, because fossils can tell us about what the world was like back when they were alive, just like how rocks can tell us the story of where they came from. Geology and archeology can work together to tell us about the world millions of years ago.
Different rocks can tell us about how that area had formed over time. As we saw on page 37, we can see the order of events based on how the rock layers are formed. According to the principle of supposition, in a controlled environment, strata is going to be put down in horizontal layers, one on top of each other. Obviously, earth is not a controlled environment, so there are many things that can mess this cycle up, like crosscutting, contact metamorphism, disconformity, and angular unconformity to name a few. This can tell us about how the earth was formed. Each layer can be dated relative to each other, or use radiometric dating to find the exact age. With the dating information along with information about the rocks and fossils found in the rocks, we can determine what the environment looked like back then.
To find the exact age of a rock you have to use radiometric dating. Radiometric dating works by radioactive decay to determine how many half lifes is has been since the sample was made. Radioactive atoms are unstable isotopes, meaning that they don’t have an equal number of neutrons to electrons. Some elements have no stable isotopes, which means that all of that specific element are radioactive, and want to decay into other elements. The process of decaying takes time. Sometimes it's lots of time, other times, it's very small. Some of the elements higher on the periodic table have half lives measured in minutes, or even seconds. These are not very useful for radiometric dating, unless you want to measure how many minutes old a sample is. You would also probably die unless you had some crazy protection, so I wouldn't recommend it. What is more useful for geologists are elements that have much longer half lives. Uranium lead dating is the most useful for geologists. They use the ratio of parent uranium to daughter lead to find how many half lives the sample has gone through. You can then convert the half lives to real years, and see the exact age of the sample.
