Your geometry is very far away from the scene origin, and the cracks are due to lack of numerical precision.
(The coordinates are made of numbers that are represented by a fixed amount of space in memory, and they have a built-in trade off between scale and specificity; that is, they can only hold so many significant digits, whether they be before or after the decimal point. So you can represent 100000, and 0.00001, but not 100000.000001.)
Basically cycles needs to make a lot of precise calculations to do its job, and your geometry is positioned so far away from the origin that all that precision has been spent (on the very large numbers of the coordinates).
The solution is to bring everything closer to the origin, either by moving your objects or scaling them down.