ARD - Geological Time Scale Lesson

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Geologic Time Scale

Planet Earth has a long 4.6 billion year history. Imagine if you were to put those 4.6 billion years in a 24 hour period. Earth formed at midnight, and then seven hours later soft bodied one cell organisms appear. Right after 9 p.m. larger complex organisms started evolving in oceans. Dinosaurs arrived around 11 p.m., but were extinct before 11:30 p.m. Humans didn't arrive until 11:59 p.m.!

4.6 billion years in a 24 hour period

Looking at the history of the Earth in days, months, years, or even centuries does not do much good because it is so vast and long. Because of this great time span, geologists use a geologic time scale to show Earth's history. A geologic time scale is a record of life forms and geologic events in Earth's history.

Scientists have developed geologic time scales by studying fossils and rock layers around the world. Using this information they have been able to place the Earth's formation of rocks in order by relative age. Later scientists were able to use radioactive dating and other techniques to determine the absolute age of the divisions in the time scale.

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