Absolute vs relative age dating dating advice for skinny guys
Just like a stack of sedimentary rocks, time is recorded in horizontal layers, with the oldest layer on the bottom, superposed by ever-younger layers, until you get to the most recent stuff on the tippy top.On Earth, we have a very powerful method of relative age dating: fossil assemblages.
When you find the same fossils in rocks far away, you know that the sediments those rocks must have been laid down at the same time.
That last, pink Precambrian column, with its sparse list of epochal names, covers the first four billion years of Earth's history, more than three quarters of Earth's existence. Paleontologists have used major appearances and disappearances of different kinds of fossils on Earth to divide Earth's history -- at least the part of it for which there are lots of fossils -- into lots of eras and periods and epochs.
When you talk about something happening in the Precambrian or the Cenozoic or the Silurian or Eocene, you are talking about something that happened when a certain kind of fossil life was present.
With this kind of uncertainty, Felix Gradstein, editor of the For clarity and precision in international communication, the rock record of Earth's history is subdivided into a "chronostratigraphic" scale of standardized global stratigraphic units, such as "Devonian", "Miocene", " ammonite zone", or "polarity Chron C25r".
Unlike the continuous ticking clock of the "chronometric" scale (measured in years before the year AD 2000), the chronostratigraphic scale is based on relative time units in which global reference points at boundary stratotypes define the limits of the main formalized units, such as "Permian".