How do scientists determine the age of a fossil?
They use several different methods. 1. Dating the things found with the fossil. 2. Checking what kind of fossils are in the same layer of sediment. (index fossils) 3. Checking changes to the atoms in the rock. Here is some information from a good web site: Paleontologists use many ways of dating individual fossils in geologic time. * The oldest method is stratigraphy, studying how deeply a fossil is buried. Dinosaur fossils are usually found in sedimentary rock. Sedimentary rock layers or strata are formed episodically as earth is deposited horizontally over time. Newer layers are formed on top of older layers, pressurizing them into rocks. Paleontologists can estimate the amount of time that has passed since the stratum containing the fossil was formed. Generally, deeper rocks and fossils are older than those found above them. * Observations of the fluctuations of the Earth’s magnetic field, which leaves different magnetic fields in rocks from different geological eras. * Dating a fos