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Geologic systems can be distinguished by their age, which refers to the timeframe in which they were formed. Geologists use a geological time scale, which is divided into eons, eras, periods, and epochs, to classify geologic systems based on their age. Knowing the age of a geologic system can help determine its historical events and relationship to other systems.

Another feature that can help distinguish one geologic system from another is the types of rocks present. Geologists study three major types of rocks: igneous, metamorphic, and sedimentary. Each type has its unique characteristics and processes that lead to its formation. Understanding the rock types in a geologic system provides information about the Earth's processes that led to the system's development.

Fossils are the preserved remains or traces of organisms that once lived. They can provide valuable information about the types of life that existed during a specific geologic time period. By studying and comparing fossils found within different geologic systems, geologists can identify changes in Earth's ecosystems and biodiversity over time.

The depositional environment refers to the conditions in which sediments were deposited to form sedimentary rocks. This environment can be identified by studying the rock's characteristics, such as grain size, sedimentary structures, and mineralogy. Different depositional environments, such as river channels, deserts, or deep-sea basins, can lead to distinct geologic systems with unique features. Studying the depositional environment of a geologic system helps in understanding the Earth's processes and climate conditions during that time. In conclusion, the main features that distinguish one geologic system from another include age, rock types, fossils, and depositional environment. By studying and comparing these features, geologists can gain valuable insights into the Earth's history and the processes involved in the formation of different geologic systems.