Dating of rocks fossils and geologic events answer
Let’s talk first about a very important idea for estimating the age of the earth: the geologic column (
From the time of the ancient Greeks, observers saw thousands of strata (layers) in the earth and hypothesized that each layer was deposited gradually over long periods of time.
And that wouldn’t be such a bad thing if they didn’t also turn right around and use the “age” of the fossils to date the rocks they are found in too!
The units commonly used for geologic age are mega-annum (Ma) for millions of years, giga-annum (Ga) for billions of years, and kiloannum (ka) ka for thousands of years.
Because these units are used according to the rules of the metric system, the M in Ma and the G in Ga must be capitalized, and the k in ka must not be capitalized.
The problem is that you cannot simply look at a rock and tell what layer it belongs to. Layers vary in thickness, are frequently missing altogether, and many of the same minerals are found throughout many layers.
It is also hard to look at a set of layers at one place in the world and figure out which part of the worldwide geologic column it belongs to.