Deep Time and Geologic Dating Explained — Earth’s Age, the Geologic Time Scale, and Radiometric Methods | Chapter 12 from Earth: Portrait of a Planet
Deep Time and Geologic Dating Explained — Earth’s Age, the Geologic Time Scale, and Radiometric Methods | Chapter 12 from Earth: Portrait of a Planet How do we know the Earth is 4.56 billion years old, and how do geologists read the history written in the rocks? In Chapter 12 of Earth: Portrait of a Planet by Stephen Marshak, we dive into the concept of “deep time”—the vast span of Earth’s history far beyond human memory. For a concise podcast summary, watch the chapter video on YouTube , or keep reading for a full educational guide. Relative vs. Numerical Age: How Geologists Define Time Geologists use two main concepts to describe time: Relative Age: Places events in order based on their position—“which came first.” Principles include uniformitarianism (“the present is the key to the past”), superposition (younger layers on top), cross-cutting relations, and fossil succession. Numerical Age: Assigns a specific age in years using radiometric dating. Geologic Princ...