Geologic Time Introduction Nearly 4 6 billion years

Geologic Time

Introduction • Nearly 4. 6 billion years have passed since Earth’s formation. • In that time, life has exploded from a few simplecelled organisms to a great variety of single-celled and multi-celled forms. • Scientists know about life’s history from studying the fossil record and rock layers worldwide. • This record can be arranged in a geologic time scale.

Organizing Earth’s History • The geologic time scale is a timeline that organizes the events in Earth’s history. 4. 6 Billion Years Ago 4 3 Prokaryotes 2 Eukaryotes 1 Today Humans • It reveals that algae, bacteria, and protozoa dominated most of Earth’s history. • More complex organisms, such as land plants and fish, evolved only within the last 500 million years. • Humans evolved only about 110, 000 year ago. • If the entire history of earth were squeezed into a single day, humans would not evolve until the last few seconds.

Geologic Time Scale • The geologic time scale is like a calendar extending from Earth’s formation to the present. The scale is divided into eons, eras, period and epochs. • Eon: The largest group: billions of years long • Era: mass extinctions mark the boundaries between the eras; hundreds of millions of years long • Period: tens of millions of years long • Epoch: divisions of the most recent periods; several million years long.

Your Geologic Time Scale • The back of your paper is divided into 4 columns • In the last or fourth column, list six to ten events in the school year in the order they will happen. For example, you may include a particular soccer game, dance, or event. • In the third column, organize those events into larger time periods, such as soccer season, rehearsal week, or whatever you choose. • In the second column, organize those time periods into even larger ones. • In the first column, organize the time period into the largest group • Go back to the 4 columns and label them as eon, era, period, and epoch • Conclusion: – List in order of smallest to largest. Epoch, Eon, Era and Period. – How does putting events into categories help you and geologists see the relationship among events?

Geologic Time Scale in a Calendar Year

Review • Why is a time scale used to represent Earth’s history instead of a calendar? • When did geologic time begin? • When does geologic time end? • Put the following words in order of smallest to largest: epoch, era, period, eon.