How old are the oldest rocks? What was the climate on Earth million years ago? When did aquatic life give way to land-based life? When did birds , conifers , dinosaurs, and flowers appear? One of the great challenges facing geologists is to find answers to such questions.
Geologic Age Dating Explained
Geologic Time: Relative Time Scale
The study of geologic time is encompassed within the larger subject of historical geology. The latter, the study of Earth's physical history, is one of the two principal branches of geology, the other being physical geology, or the study of Earth's physical components and the forces that have shaped them. The background of historical geology is discussed in some detail within the Historical Geology essay. Its principal subdisciplines include stratigraphy, the study of rock layers, or strata, beneath Earth's surface; geochronology, the study of Earth's age and the dating of specific formations in terms of geologic time; sedimentology, the study and interpretation of sediments, including sedimentary processes and formations; paleontology, the study of fossilized plants and animals; and paleoecology, the study of the relationship between prehistoric plants and animals and their environments.
Geological Time Scale
Stephen A. Relative time does not tell how old something is, all we know is the sequence of events. Thus we can say how old something is. By carefully digging, we have found that each trash pit shows a sequence of layers.
How many year's is a "long time"? We often express time in hours or days, and 10 or 20 years certainly feels like a long time. Imagine if you needed to think about one million, million, or even several billion years. These exceptional lengths of time seem unbelievable, but they are exactly the spans of times that scientists use to describe the Earth. The Earth is 4.