地质学家如何对岩石和化石进行定年？ Geologists use a variety of methods to date rocks and fossils, providing important insights into the Earth's history. One common technique is radiometric dating, which involves measuring the decay of radioactive isotopes in a sample. By comparing the amount of parent and daughter isotopes present, scientists can calculate the age of the rock or fossil. Another dating method is stratigraphy, which relies on the principle of superposition. This principle states that in undisturbed layers of rock, the oldest layer will be at the bottom and the youngest at the top. By examining the sequence of layers, geologists can determine the relative ages of rocks and fossils. Paleontologists also use biostratigraphy to date fossils based on the known ages of the organisms they come from. By correlating the presence of certain index fossils with specific time periods, scientists can establish the age of a fossil bed. By combining these dating methods, geologists can create detailed timelines of Earth's history and better understand the processes that have shaped our planet over millions of years.