How old is the earth?

Part 1 (of 4)

https://www.youtube.com/watch?v=uJGairhrPGc

Part 2 (of 4)

https://www.youtube.com/watch?v=f1Qr9ZZ-Y30

Part 3 (of 4)

https://www.youtube.com/watch?v=xc-qInfV174

Part 4 (of 4)

https://www.youtube.com/watch?v=txEoErEWdaI