This document summarizes key developments in determining the age of the Earth and the evolution of geological timescales. It discusses early Greek thinkers who realized fossils were remains of ancient life and estimated the Earth was many thousands of years old. In the late 1700s, scientists used methods like salt accumulation in oceans to estimate ages of 90 million years. In the late 1800s, physicists calculated ages of 20-40 million years using heat flow, upsetting biologists. Radioactive dating in the 1900s proved the Earth was older than prior estimates, supporting Darwin's theories of evolution over long periods. The development of modern geological timescales divided Earth's 4.56 billion year history into eras, periods, and epochs based on fossil evidence

1. Historical Geology Chapter 12 Geologic Time

24. Distance is 12 miles between these two rock units

25. Distance is 17 miles between these two rock units

32. Fossil Types

59. Bristlecone Pine

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