1. D39 Earth Time

2. D39 Earth Time Background 1
The Earth is over 4 billion years old.
Modern humans have only been around for 100,000 years, or 0.1% of Earth’s history.
Paleontologists: scientists who use evidence from rocks and fossils to understand when events occurred in the history of life.
They study radioactive decay in rocks & fossils to figure out when things happened.

3. D39 Earth Time Background 2
Six of seven volcanoes in the Yucca Mountain area last erupted between 385,000 years and one million years ago. The remaining volcano was active within the last 75,000 years.
All of these time periods are very long compared to the average human lifespan.
Geologic Time: how paleontologists refer to thousands, millions, and billions of years.

4. D39 Ordering Events (copy in lab book)
Events on Earth:
Original Order
Time Period
Revised Order
Recent: Less than 50 million years ago
million years ago
million years ago
Oldest: More than 500 million years ago

5. D39 Earth Time Procedure 1 Get the Ordering Events worksheet.
Imagine that your friend is studying to be a paleontologist. She asks you to help her list some events in the history of the Earth in order. She’s interested in organizing her ideas into four time periods.
With your group, read the information on the front of each “Event on Earth” card carefully.

6. D39 Earth Time Procedure 2
With your group, place each event in order from oldest to most recent. Hint: If you need help, read the clue on the back of the card. Some clues will help you put the events in order while other clues will help you identify the time period in which an event occurred.
Remember to listen to and consider the ideas & explanations of other group members. If you do disagree with the others, explain why.

7. D39 Earth Time Procedure 3
Discuss with your group during which time period you think each event occurred.
On the worksheet, record the order of events that your group decided on, and put each in the time period you think it occurred.
Next, your teacher will show you a copy of the correct order of each event.
Rearrange your cards and record the revised order on the worksheet.

8. D39 Earth Time Analysis: Date______ Name____________________ Hour__
Answer each question using 1 paragraph.
How did your group’s original order of events differ from the paleontologist’s? Explain
Would it be useful to measure Earth’s history in minutes and hours? Why or why not?
Some nuclear waste can be radioactive for 250,000 years. Is this a long or short period in geologic time? Explain.
Some movies show humans playing with dinosaurs. Explain if this is possible or not.