25 March 2015
With the Universe being 13.9 billion years old, and recognizing the significant events described elsewhere on these pages, the scaling and descripition of the various stages in the Earth’s history is difficult since it involves very large time spans, compared to the very short history of the Earth, which is mostly within 4.5 billion years. Many changes have obviously occurred in order to come from the Big Bang to the big blue planet that we are today. (Spearing. 1991).
To work with these time frames and events, geologists have defined several eras as follows: Cenozoic (now to 66 million years); Mesozoic (previous to 345 My); Paleozoic (to 570 My) and Precambriam (to 4.5 billion years}. Ages of the various rocks are determined with carbon dating techniques where the analyzed state is the final, stable state existing at the time of the dating. The time of Human effects on the Earth have been very recent and are identified as the Holocene age of up to 11,700 years preceded by the Upper and Middle Pleistocene, Calabrian and Gelasian up to approximately 2.6 Million years. In these periods, geologists have identified time periods when significant land use occurred and expanded (roughly 5,000 years). Other much more recent time spans are when large dams were constructed and when water began to be largely used as well as fertilizer. These are all in the Anthropocene epoch at the top of the Holocene. (Monastersky, 2015).
Click below to watch an interesting video on the geological times,