To start with it should be pointed out that the main part of the series were broadcast on Wednesdays, but the slightly off-topic ones were broadcast on Saturdays. However, the first of those was claimed to be broadcast a few days before the final regular episode was. The second one being then broadcast two weeks later (Wikipedia being the only source of information about broadcast dates).
Episode 9 (Deep trouble – The scientists’ view of future prospects) first aired on 28 October 2001.
The final episode (Making waves – The making of the series) first aired on 11 November 2001.