How Long is Long?

The earth formed along with our solar system around 4.6 billion years ago. This idea of ‘billions of years’ is a foreign concept for humans in that we are used to measuring time in minutes, hours, or days. This lab is designed to place geologic time into this human perspective. The goal is to illustrate how vast geologic time is by comparing geologic time with the simple task of counting to 100.

The following timeline provides some major events in human history and the evolution of life. You will use this timeline in later sections of the lab.

Years before Present

250 Founding of the U.S.

2750 Founding of Rome

3800 Construction of Stonehenge

9000 Founding of Jericho, the World’s First City

17,000 First Humans enter North America

30,000 Modem Humans enter Europe

100,000 First Anatomically Modem Humans

500,000 Homo erectus Discovers Fire

3,500,000 First Bipedal Human Ancestor (Australopithecus)

66,000,000 Extinction of the Dinosaurs

425,000,000 Arthropods are the First Organisms to Live on Land

540,000,000 Cambrian Explosion in the Diversity of Life forms

4,000,000,000 First Life on Earth

4,600,000,000 Earth is Formed

I. First you need to determine your scale of comparison. This is the human scale you are going to use to compare with the geologic time scale. For this exercise we are going to use the time it takes you to count to one hundred.

First, record the time it takes you to count to 100 (in seconds):

Time: ________ 60 seconds _________

This time to count to one hundred is your human time scale. The time elapsed while you counted to one hundred was probably somewhere between 30 and 60 seconds. This is a time scale that you can relate to, especially considered you just experienced it! You are familiar with this amount of time and you are comfortable with discussing events (like counting) that can occur over a period of 30 to 60 seconds.

Now you are going to start converting the human scale to the geologic scale. For the purposes of this exercise, you are going to consider each 100 years along the timeline provided above as equivalent to the time it takes you to count to 100. So, counting to 100 equals the passage of 100 years. Let’s convert our dates before present to counting times (fill in the blanks):

1. Founding of the U.S.-Years before present (B.P.):_250__

To convert this to counting episodes, first divide this number by 100:___2.5___

This is the number of times you would need to count to 100 in order to replicate 250

years of geologic history in your human scale. Now, convert this to seconds using your time to count to 100. Do this by multiplying your counting time by the number counting episodes.

Human Scale (in seconds):_150__

This human scale is the amount of time you would have to count to reach the founding of the United States at your new scale. Now, perform these conversions for each of the other events on the timeline (fill in all the blanks):

2. Founding of Rome-Years B.P.____2750_____;# of counting episodes____27.5__;

human scale (in seconds)_____1650_________

3. Construction of Stonehenge-Years B.P.___3800___;# of counting episodes___38_____;

human scale (in seconds)________2280________

4. Founding of Jericho-Years B.P.___9000____;# of counting episodes___90______;

human scale (in seconds)_______5400________

5. First Humans in North America-Years B.P.__17000___;# of counting episodes 170__;

human scale (in seconds)___10200__________

6. Modern Humans in Europe-Years B.P.__30000___;# of counting episodes _300_;

human scale (in seconds)____18000_____

7. First Modern Humans-Years B.P._100000___;# of counting episodes __1000__;

human scale (in seconds)______60000_____

8. Discovery of Fire-Years B.P._500000___;# of counting episodes__5000____;

human scale (in seconds)_____300000________

9. Evolution of Bipedal Apes-Years B.P._3500000__;# of counting episodes_35000_;

human scale (in seconds)____2100000__

10. Extinction of Dinosaurs-Years B.P.__66000000_;# of counting episodes__660000__;

human scale (in seconds)___39600000_____

11. Arthropods Colonize Land-Years B.P._425000000__;# of counting episodes__4250000__;

human scale (in seconds)___255000000____

12. Cambrian Explosion-Years B.P._540000000_;# of counting episodes__5400000__;

human scale (in seconds)____324000000____

13. First Life on Earth-Years B.P.__4000000000__; # of counting episodes_40000000__;

human scale (in seconds)__2400000000___

14. Formation of Earth-Years B.P.__4600000000__; # of counting episodes__46000000_;

human scale (in seconds) 2760000000 –

Remember, the human scale represents the number of seconds you would have to be counting to arrive at a given event. Most people consider the founding of the United States or the founding of Rome to have occurred a long time ago. How do these dates compare with the time between now and the first appearance of humans?

If human (pre)history began with the evolution of the first anatomically modem humans, how does this length of time compare with diversification of life forms marked by the Cambrian explosion?

How does the length of time between now and the Cambrian explosion compare with the length of time between now and the formation of the Earth?

Place humans within the perspective of Earth’s history? How does human history compare with Earth’s history? Can geologic time inform us about our own place in the world? Given that 99.9% of all species that have ever lived are now extinct, what might Earth’s history teach us about our own future?