Why didn't the early geologic time scale include the number of years ago that events happened?
Geologic time is only approximate.
The early geologic time scale did include the number of years ago that events happened. The timeline, based on carbon dating, is approximate however.
Shygirl and Ms. Sue are correct...
The early geologic time scale didn't include the number of years ago that events happened because at the time, scientists didn't have the tools or methods to accurately determine the age of rocks and fossils. Instead, they relied on relative dating techniques, which involved comparing the ages of different rock layers and fossils using principles like superposition and fossil succession.
Relative dating allowed scientists to establish a sequence of events and determine the relative order in which they occurred. For example, they could determine that one layer of rock was older than another layer based on the positions of the fossils found in each layer.
However, it was not until the discovery of radiometric dating in the early 20th century that scientists were able to assign numerical ages to rocks and fossils. Radiometric dating involves measuring the ratios of isotopes in certain rocks and minerals to determine how long it has been since they formed. This method allows scientists to calculate the actual number of years that have passed since a particular event occurred.
So, the early geologic time scale did not include specific years because the technology to determine accurate numerical ages had not yet been developed. It wasn't until later advancements in radiometric dating that scientists were able to refine the geologic time scale and provide precise numerical ages for the events in Earth's history.