Some time ago Callan Bentley collected a few nice geological analogies. I instantly liked one of those, found in the comments: earth history as a human arm.
I think that the arm is a clearer illustration than e.g. using the “one year of earth history is one second” approach (where the age of the earth would be 146 years) or comparing it to the human life span. 146 years or your complete life are not so easy to visualise, in my opinion. Also, you can easily carry your arm around and show “You are here.” on it as necessary. 😉
Earth history as a human arm, with the contact between the neck and the shoulder being Earth's origin:
The shoulder is the base of the Archean.
The elbow is the Archean/Proterozoic boundary.
The wrist is the Proterozoic/Phanerozoic boundary (with the bulge of the lower forearm being about where the Ediacaran begins).
The palm is the Paleozoic.
The first two digits of the middle finger is the Mesozoic.
The last digit of the middle finger is the Cenozoic, and a single pass of nail file eliminates the history of Homo sapiens.
If you measure and calculate this, you'll recognise that geological time spans and body don't match well from Phanerozoic/wrist onward: The Phanerozoic should start only at the knuckles and the younger ages move closer to the fingertip accordingly. I have drawn it that way in my picture above – hopefully correctly.
Using my arm length of 85 cm, measured from the contact shoulder/neck to the tip of the nail of the middle finger, I get these figures:
|Ma||cm||Age||Event||Place on arm|
|0.01||0.0002 (2 µm)||Neogene||end of the last ice age|
|0.16||0.003 (30 µm)||oldest Homo sapiens||“nail file”|
|17||0.3||formation of the 2nd Lusatian lignite
|near the edge of the fingernail|
|65||1.2||Paleogene||base of the fingernail|
|251||4.6||Mesozoic||first finger joint|
|ca. 600||11||Proterozoic||Deposition of the Lusatian Greywacke2||beginning of knuckle|
|1000||18||formation of Rodinia / Grenville orogenesis||wrist|
|3800||70||Archean||contact between arm and shoulder|
|4280||79||Hadean||oldest known rocks||on the shoulder|
|4600||85||formation of the earth||contact between shoulder and neck|