1. 1Daily Warm-Up Exercises Day 31 About how long has Earth existed? Earth has existed for about 4.5 billion years (or 4,500 million years). About how long have human beings (Homo sapiens) existed? Humans have existed for about 200,000 years.

2. 2 VERY IMPORTANT!!!  Scale: 1 million years = 1 millimeter  All measurements must be made from the Now line.  The zero end of the ruler must always stay on the Now line.

3. 3 Mark Eras  When you finish all the periods, go back and draw a heavy line to mark the beginning of each era.  Label the era by writing its name across the periods.

4. 4 Add Grand Canyon Rocks  Turn to Rocks Over Time, on page 52 in your lab notebooks.  This table lists the time periods during which these rock layers formed.  For example, the ocean in which the Kaibab Formation was deposited existed between 260 and 255 mya. How long did the Kaibab Sea exist? 5 million years

5. 5 Add Grand Canyon Rocks  Add these rock layers to your time line.  Label and color each area.