On The Cosmic Calendar, A Date To Remember

Carl Sagan, describing his twelve-month capsule of the history of the cosmos, summarized its lesson this way: “The world is very old, and human beings are very young.”  But a neglected date on the calendar points to a different conclusion about organic life itself.

Sagan included “The Cosmic Calendar” in The Dragons of Eden in 1977. The first voyage to Mars had lifted off two years earlier. NASA, with Sagan’s help, began listening for and sending messages to other intelligent beings who might have been out there. Sagan, while asking readers to appreciate our amazing intelligence, at the same time believed that we were not the only creatures in the universe who were so endowed. The Cosmic Calendar helped him show that because it took eons to produce human civilization, the eons might have led to similar results elsewhere.

On the Calendar, one month represents about 1.1 billion years, one day equals 38 million years, and in one brief second, 438 years fly by. The Big Bang, 13.8 billion years ago, explodes on January 1. The Milky Way takes shape around March 11 (dates are from the Wikipedia version) and our Sun first shines on September 2, with planets soon after. The first living cells stir on September 21. October features photosynthesis, the gradual oxygenation of the atmosphere, and the persistence of simple bacteria and their cousins. In November, those single cells develop nuclei, complexity, and greater energy, leading to the first multi-celled organisms in early December. From then on, the variety of life emerges swiftly: fish and land plants in mid-month, dinosaurs at Christmas, then birds and flowers, and humans in the last hours of New Year’s Eve.




But this late appearance of humans may distract us from another date. September 21 marks the date for the beginning of organic life itself, only a few “short” weeks (about 700 million years) after the formation of the planets. From that date on—for more than a quarter of the duration of the universe—life has existed on Earth. While humans may be newcomers, living things are not. Our chain of ancestors are long-time participants, old-timers in the cosmos. We humans are fully part of the long cosmic process, not just because our atoms are star-stuff but because our cells have their “months” of cosmic history.

What is new in us, with our nearly-New-Year’s intelligence, is that we are aware of all this. But our living spark is nearly as old as planets.

Shall we celebrate September 21 each year as the “Birthday of Life”?

6 thoughts on “On The Cosmic Calendar, A Date To Remember

  1. It is Intersting to include some of the future in the Cosmic Calendar. For intance, if you include the estimated 150 trillion years of star formation that has yet to happen then the 13.8 billion years that have happened to date happen in the first 48 minutes 23 seconds after midnight on January 1st.

    • Whoa, that’s an interesting idea! Including a future of any length within the calendar of all time is quite a thought.

      The current version is, essentially, big history intended to put certain events in perspective. What would be the purpose of including such a huge future whose contents we don’t know in detail?


      • The point I think is to give perspective of another sort. We often hear about doom and gloom futures that make the future seem short and without a lot of possibility. At the same time Big History dwarfs us makes us feel small. The overall effect is to make us feel small and helpless and hopeless. Realizing that there is time to try everything that has ever been tried by evolution, by stellar evolution, by living beings again and again, in all different ways, tens of thousands times, reminds me that the future is almost assuredly bright, if not for Earth Life, then for Life as a whole.


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