Ancestors of Gods: Geologic Time Analogies

Radiometric dating indicates that the Earth is about 4.570 billion years old. Geologists break down this 4.570 billion years time frame into a calendar as shown below.

Some people have a hard time getting their arms around this number (4,570,000,000); so today, I thought I would help give you a perspective of how much time 4.570 billion years really is.

At a recent symposium which I attended, Dr. Kirk Johnson of the Denver Museum of Nature and Science attempted to help us get a grasp of time by telling us a million years was about the time it would take for your fingernails to grow to the length of 18 miles. Further calculations show that if you were alive when our solar system was created, your fingernails would now be 82,260 miles long. That would long enough to circle the Earth more than 3 times. I bet you didn’t know that!

The analogy for geologic time that I used in my book, Ancestors of Gods, uses the length of one’s arm span as a scale of time. Holding your arms out to your sides; if the tip of your left hand represents when the earth was first formed and the tip of the middle finger on your right hand represents the present, then life first appears on earth about at the bend of your left elbow. From there to about your right bicep, life consisted of single celled organisms, mostly bacteria. At about your right bicep, the first eukaryotes, single celled organisms with nuclei, appear. The first multicellular organisms don’t appear until about two inches above your right wrist. The first fish appear at about your right wrist bone, the first reptiles at the center of your right palm, and the first mammals at the base of your middle finger. The extinction of the dinosaurs occurs near the last joint in your middle finger. If you were to take a nail file and make a light pass over the fingernail on the middle finger of your right hand, you would eliminate modern man’s time on earth; two passes would eliminate the entire history of hominids, man’s entire post-ape-ancestor lineage.

Included below are a few other interesting analogies:

1. 365 days/1 year analogy

For this analogy we assume the Earth was formed on January 1^stand the present is midnight on December 31^st. The oldest known rocks, 3.9 billion year old metamorphic rocks from Greenland, would date from late February. Oxygen would first appear on Earth on July 25^th. Multicellular life with skeletons would appear in late November and the first mammals would appear on December 15^th. The Atlantic Ocean would begin to open up, separating North America from Europe, about December 19^th and the dinosaurs would die out on 27th. Homo sapiens would first appear at 11:49PM on December 31^stand the birth of Christianity would occur at 11:59PM.

2. Trips around the Milky Way Galaxy

The Earth has circled the Milky Way Galaxy 18 times since its conception 4.6 billion years ago. About 2/5’s of an orbit ago, the dinosaurs died out. Almost 2 orbits ago, the first fish appeared on Earth. Multicellular life appeared about 4 orbits ago. (from http://www.vendian.org/mncharity/dir3/ geologic_time_galactic/)

3. The toilet roll analogy

For this analogy, you need a class in an auditorium. A student starts at the front of the auditorium at the present time. As the student slowly walks toward the back of the auditorium and back in time, she unrolls the toilet paper. By the time the student gets to the back of the auditorium, she stops to recognize the time the very first dinosaurs begin to appear on Earth. The student has covered about the last 5% of the Earth’s existence. The student continues across the back of the room and heads down another aisle to the front of the auditorium. By the time she gets back to the front of the auditorium, she has only gone back about 10-15% of the way back to the origin of the solar system. There are still quite a few sheets on the roll of toilet paper.

4. The glass of beer analogy

(from http://jrscience.wcp.muohio.edu/lab/GeoTime.html)

I think the students probably came up with this analogy after class on a Friday night.

Now it is your turn. Please leave your favorite analogy or make up one of your own in the comments. To help you make one up, I have included below a time line for the various highpoints in the evolution of the Earth.


Years Ago	Event
4,600,000,000	Origin of the Earth
3,900,000,000	Oldest Dated Crustal Rocks
3,800,000,000	Oldest Evidence for Life
2,000,000,000	First Oxygen Atmosphere/Ozone Layer Forms
900,000,000	Oldest Metazoan Fossils
510,000,000	Oldest Fossil Fish
458,000,000	First Land Plants
375,000,000	That important first step: Amphibians Evolve
245,000,000	Huge Mass Extinction at End of Permian Period / Close of the Paleozoic Era
200,000,000	First Mammals
160,000,000	First Birds
145,000,000	Atlantic Ocean first opens
130,000,000	Angiosperms (Flowering Plants) on the Scene
65,000,000	Adaptive Radiation of Mammals
	Dinosaurs Go Extinct
	Close of the Mesozoic Era/ Beginning of the Cenozoic Era
3,400,000	New discoveries of Australopithecus afarensis (Lucy) fossils from Ethiopia
2,000,000	Pleistocene Ice Age begins
2,000,000	Light from the Andromeda galaxy seen today left Andromeda
600,000	Age of Homo erectus fossils from Ethiopia
125,000	Oldest rocks in the Bahamas
100,000	Homo sapiens appears in the fossil record
15,000	Last ice sheet retreats from northern United States
7,000	Grahams Harbor, San Salvador, Bahamas floods due to rising sea level after ice sheets are reduced to modern day volume
506	Columbus lands in New World
(from http://www.earthsciweek.org/forteachers/geotime_cont.html)