One of the better early ideas at dating the planet came from the ever-reliable Edmond Halley, who in 1715 suggested that if you divided the total amount of salt in the world’s seas by the amount added each year, you would get the number of years that the oceans had been in existence, which would give you a rough idea of Earth’s age. The logic was appealing, but unfortunately no-one knew how much salt was in the sea or by how much it increased each year, which rendered the experiment impracticable.
Dating earth - Salt in sea method
