Thread by @AdamRutherford

Happy birthday to THE EARTH! 23rd October is the 1st day of creation for most biblical Creationists.
God said γενηθήτω φῶς - let there be light - exactly 6023 years ago, according the chronology of Bishop Ussher. Though absurd, it is not without interest. A thread: 1/n

Ussher, a 17thC Primate of All Ireland, worked the date out in Annales Veteris Testamenti via a literal reading of the Bible. It was a major concern of theologians at the time (including Bede and Kepler), many also came up with a similar sort of number, around 6-7kya. 2/n

This is absurd cos we know now that the Earth is more like 4.54 billion years old (see below). At the time of Ussher’s date of creation, agriculture was blossoming, ploughs in Europe, maize cultivated in the Americas, copper forged in Egypt, pastoralism in Africa. 3/n

I will defend Ussher here, as he was methodical and careful about this date, taking into account details such as Josephus putting the death of Herod in 4 BC, and thus Jesus' birth being 5 BC, in order for the Matthew Gospel to be correct. 4/n

Ussher’s chronology, whilst more than 5 orders of magnitude wrong, was calculated with accepted wisdom of his time, and applied it rigorously to come up with his number. What is madness is to cling to this methodology and date in the 21st C, as some Christian creationists do. 5/n

Many other cultures also had a stab at dating the Earth, e.g. the Chinese god-creator Pangu did it around 36kya. 6/n

Some of the stories are rather more graphic than the Biblical account. There’s Atun, the self-created Egyptian god who performed autofellatio and spat out his seed to create the world. 7/n

Avid #curio @Stephenfry covers Greek origin stories in Mythos, with all the deliciously sordid details, baby-eating semen-flinging genital-slicing Cronus, that sort of thing. 8/n

In Finnish lore, Ilmatar the daughter of the sky, floats for centuries, until the sea impregnates her. Then she sits down and a bird lays a giant egg on her knee. But it gets hot and falls off, and breaks, and forms the sun and the Earth. 9/n

The Earth is actually around 4.54 billion years old. We know this via several methods, but most elegantly via radiodating of zircon – also used in cheap jewellery. Zircon incorporates an atom of uranium into their crystal structure, but cannot trap lead.
10/n

A proportion of Uranium is radioactive, and once trapped, a clock starts, as U238 degrades to make an atom of lead, with a half-life of 4.47 billion years. Zircon crystal are mighty tough, so last through geological metamorphoses. 11/n

Any lead Pb207 found in zircon therefore began its entombment as U238, and by working out the proportions of Pb207 in a zircon deposit, we can tell how old it is. Crystals from Jack Hills in Western Australia have given a date of 4.404 billion years since their formation. 12/n

So anyway, there you go. Ussher's evidence base was faulty, not his methodology.

I am on a train, and was a bit bored. That is all. 13/13

Addendum: I did not know this but my excellent pal @rmathematicus wrote a blog about Ussher a decade ago, and it much more scholarly and interesting than my efforts above. 14/13
bit.ly/2W6xf7k