Time Machine - Will it overwrite backups?

[bp1000]

I have just erased my MBA's SSD and re-installed a fresh copy of Mountain Lion, set up all programs from scratch etc.

If i enable time machine on the same external disk will it overwrite my previous backups?

I would like the option to go back to my pre-erased config if i need to, is this possible?

Thanks

 

[Risco]

Nope, it will continue where it left off