Earth Day

 

   Happy Birthday Earth! According to my calculator, you are now 6030 years old. You've crammed a lot into six millennia. My greetings today are based on the studies of Bishop James Ussher of Dublin and London (1581-1658). We use methods not available to Ussher to arrive at an earlier date for the creation of the earth. Ussher did well with the tools he had to work with, which was mainly the Bible. 

   Starting from 4 BC, which he correctly realized was the year Jesus was born, he worked backwards using Jesus' genealogies to 4004 BC. He chose October 23 as the date because he believed everything must have started on the Autumnal Equinox (England's calendar was off a bit in Ussher's day). First he picked midnight on the 23rd for the start, then he backed it up to 6:00 pm on the 22nd. This must have been when the Big Bang took place, which Ussher could not have been expected to know about.

    Before we scoff at Ussher, we should recall that Isaac Newton agreed with Ussher's date. The 4004 BC date was accepted for two centuries until Lord Kelvin theorized the earth was 400 million years old based on the cooling of the earth. He had guessed correctly that the earth was initially in a molten state. Kelvin then guessed earth's temperature had been 7000°F. He was 3000° too high. His guess of a 400 million year earth was at least in the ballpark, but as he refined his theory, he moved in the wrong direction, ending up saying earth was only 20 million years old. For his efforts he had a temperature scale that starts at absolute zero named after him.

   The next big leap backward came with the discovery of radiometric dating in the early 1900s. Scientists realized that earth must be billions rather millions of years old. In 1956, the geochemist Clair Patterson determined the age of the earth to be 4.55 billion years old. This age has since been whittled back to 4.54 billion years give or take 40 million years. 

   Patterson used the rate of uranium decaying into lead to find the age of the earth. It was simple once he and some friends figured out how to do it. The problem was that he couldn't use the rocks on earth because they had all been melted at some point in their past. So he found a meteorite in Arizona which would have formed the same time that earth did. The meteorite he used had fallen out of the sky about fifty million years ago. While working with lead Paterson realized how toxic it is and led the charge to get lead out of gasoline. What a guy! Patterson was born in Des Moines, a city which has produced such worthies as Bill Bryson and WannaskaWriter.

   If Bishop Ussher could return to earth, I'd show him the latest research on the age of the earth. I'd let him get used to the idea before telling him about the Big Bang which occurred 13.8 billion years ago. I'd tell him it happened on October 23 to ease the shock.

All of time viewed as a single year.
https://en.wikipedia.org/wiki/Cosmic_Calendar#/media/File:Cosmic_Calendar_(extended_by_%22The_Final_Second%22).png