Thanks for downloading the In Our Time podcast. For more details about In Our Time and for our terms of use, please go to BBC.co.uk.

I hope you enjoy the program.

Hello, we used to be very clear about the origin of the Earth. Bishop Usher in 1654 arrived at an exact

figure and specified it in his work Analese veterans at Novi Testamenti.

He deduced that the work on planet Earth began at exactly 9 a.m. on Monday the 23rd of October,

4,04 BC.

The date was then printed in the margin of the Bible and preached from the pulpit right up to the 19th century to the left of in the beginning was specified before Christ

2004.

Christian believers thought that the creation story was solid as a rock until the geologists

arrived and how solid our rocks these days.

First Hutton, then Smith and then Lyle smashing away at Orthodox belief in a way that made poor Ruskin

quail, but in doing so they created a science.

With me to discuss the development of geology and our changing understanding of the

structure of the earth is Simon Winchester, author of The Map that Changed the World, a tale of William Smith and

the Birth of a Science.

Also with us is Cherry Lewis, geologist and author of The Dating Game, one man's search for

the age of the earth, and John Cosgrove structural geologist from the

Royal School of Mines at Imperial College London.

Cherry Loes, can you give us some idea of where geology was up to the 18th century?

Yes, I think what you've just said about Archbishop Busha

is really important because it puts in context the religious climate that was prevailing through certainly the 17th

and 18th centuries that really dominated the understanding of geology. I think perhaps if we start with somebody

...