what is deep time?
http://en.wikipedia.org/wiki/Deep_time
Deep time refers to the concept and timescale used in geology and other scientific disciplines to describe the vast expanse of time that has occurred since the formation of the Earth. It encompasses billions of years of Earth's history, spanning from the formation of the planet approximately 4.6 billion years ago to the present.
To understand deep time, scientists use various methods and techniques to estimate the age of rocks, fossils, and other geological features. Here are a few key processes used to determine Earth's age:
1. Radiometric dating: This method utilizes the radioactive decay of certain elements found in rocks and minerals. By measuring the ratio of parent isotopes to daughter isotopes, scientists can calculate the amount of time that has passed since the rock formed.
2. Stratigraphy: By studying the order and arrangement of rock layers, scientists can determine relative ages of different geological formations. This technique relies on the principle of superposition, which states that younger rocks are typically found on top of older rocks.
3. Fossil dating: Fossils provide valuable clues about Earth's history. By examining the type and distribution of fossils in different sedimentary layers, scientists can establish a relative timeline of when different species lived and track changes in biodiversity over time.
4. Geological processes: Understanding the rates at which geological processes, such as erosion, deposition, and mountain building, occur helps scientists estimate the amount of time required for certain geological features to form.
By combining these methods and many others, scientists have been able to reconstruct Earth's history and develop a comprehensive understanding of the immense timescale encompassed by deep time.