Cosmic Second

The sheer scope of cosmic, geological, and evolutionary time is hard for human understanding to truly grasp.

Carl Sagan made an famous metaphor with what he called the "cosmic calendar" which the history of the known universe is reduced to a single year. The start of the Big Bang was on January 31. Dinosaurs first appeared on Christmas Eve and the non-avian dinosaurs got wiped out on December 29. Columbus made landfall in the New World on December 31 at 11:59 PM at one second before midnight. Via YouTube, here is how Sagan described the Cosmic Calendar on his 1980 series Cosmos (4 minutes: 52 seconds):







When Sagan made the series he knew the universe was around 15 billion years old give or take quite a bit. The current estimate is 13.7 billion years so the dates given by Sagan are still in the ball park except for the formation of our Milky Way Galaxy which happened earlier than was thought in 1980. A more modern (and non-video) version is The Universe in One Year from the Discovery Channel and the American Museum of Natural History.

In this post I suggest a different metaphor for deep time: the cosmic second.

The Earth is approximately 4.55 billion (4,550,000,000) years old. Just how big of a number is 4.55 billion? There is not one person in the entire world who has lived as many seconds as the number of years the Earth has existed.

One year is 31,558,150 seconds¹ thus one billion seconds is 31.687536 years. I will define a "cosmic second" as one Earth year. The following table gives just how long ago certain events were in terms of cosmic seconds:

Event	Years ago	Cosmic second timescale
One year ago	1	1 second
Creationist age of universe	Under 10 thousand	2.8 hours
Lucy	3.2 million	37 days
Extinction of the dinosaurs	65.5 million	2.1 years
First known mammal- like reptiles	320 million	10 years
Start of the Cambrian	542 million	17.1 years
Formation of the Earth	4.55 billion	144 years
Big Bang	13.7 billion	434 years

A bit under 3 hours compared to over four hundred year is how a young-earth creationist timescale corresponds to reality. Think of it. Four hundred years ago is before the Mayflower landed in Plymouth in 1620. Thus the number of seconds since the Pilgrims settled in what is now Massachusetts is considerably less then the number of years since the Big Bang.

Ninety years which most would consider to be a long life, is only a minute and a half in terms of the cosmic second. Most people today have been around less than a minute according to this timescale compared to 144 years for the Earth. Compared to deep time, a human life is a brief precious moment -- if you blink, you will miss it.

Note: I am sure someone had to used this metaphor before me. I hope someone has since it seems to obvious to me. But I don't recall offhand anyone else using this to explain just how deep time is. If someone has done this before, I certainly don't mean to step on anyone's toes.





1. I am using the sidereal year so we don't have to worry about leap years and other calendar issues and thus consider a year to be how long it currently takes the Earth to make one orbit around the Sun.