A billion seconds ago it was 1957.
A billion minutes ago it was the time of Jesus.
A billion hours ago it was the time of the Stone Age.
A billion days ago nothing walked on the earth on two feet.
How many is a billion?
In British English, a billion used to be equivalent to a million million (i.e. 1,000,000,000,000), while in American English it has always equated to a thousand million (i.e. 1,000,000,000). British English has now adopted the American figure, though, so that a billion equals a thousand million in both varieties of English.
The same sort of change has taken place with the meaning of trillion. In British English, a trillion used to mean a million million million (i.e. 1,000,000,000,000,000,000). Nowadays, it’s generally held to be equivalent to a million million (1,000,000,000,000), as it is in American English.