How were divisions of time separated when scientists created the geologic time scale?
by the thickness of rock strata
by the color of rock strata
by the fossils found in rock strata
by the location of rock strata
I think it is by the fossils found in rock strata.
When scientists created the geologic time scale, they separated divisions of time primarily based on the fossils found in rock strata. This is because different fossils are found in different layers of rock, and certain fossils are unique to specific periods of time. By studying the types of fossils present in different layers, scientists were able to establish a sequence of time periods and classify them accordingly.
To determine the divisions of time, scientists first observed the rock strata and identified the fossils within them. Fossils are the preserved remains or traces of ancient organisms, such as bones, shells, or imprints. By analyzing the fossils found in the rock layers, scientists could determine the age and relative time period of each layer.
For example, certain fossils called index fossils are known to exist only within specific time periods. These fossils are used as markers to define and correlate the different divisions of the geologic time scale. When an index fossil is found, scientists can be confident about the relative age of the rock strata containing the fossil.
Other factors such as the thickness and location of rock strata can also provide additional information for determining the geologic time scale. However, it is primarily the fossils found within the rock layers that serve as the key factor in separating the divisions of time.